1. hand crossbows have the light property, yet the only purpose of light weapons is to engage in two weapon fighting, something the hand crossbow cannot do since the rules on two weapon fighting states that you can only use two weapon fighting with melee weapons, making the light property pointless for purposes other than flavor and any potential future features that synnergize with light weapons, of whom there are none currently.
2. the dueling fighting style has the requirement of having an one handed melee weapon in one hand and no other weapons, and it grants an bonus to damage rolls, regardless of what type of attack you make with it. This means that you could use this fighting style with thrown weapons like javelins and spears. combining this fighting style with the thrown weapon fighting style can lead to an rather interesting 10th level champion fighter who deals just as much damage on average throwing an puny javelin with one hand as when he uses an mighty greataxe with two hands
3. the only mechanical difference between spears and tridents is that spears are simple weapons and tridents are martial weapons, however the only feature in 5e dnd that applies to martial weapons that does not apply to simple weapons is the martial traning feature of the hobgoblin. Some magic weapons are of course trident exclusive like the trident of fish command, and some races to of course get free trident proficiency, but the martial traning racial trait for the hobgoblin is the only time where the trident as an weapon is preferable to the spear on its "own merit" so to speak
4. the net is the only weapon with no damage type associated with it (at least not in the sourcebooks, on dnd beyond it deals 0 bludgeoning damage), meaning that you could potentially cast conjure barrage with an net as your material component and deal 3d8 damage with no associated damage type, or cast an spell that deals no damage depending on your interpretation of the spell 

Summary: I think most if not all of these have been discussed.

1. Could be useful if some new option requires the 'light' property on a weapon and also allows crossbows.
2. Yea, so? This implies that there is no difference between "wielding a melee weapon" and "throwing a thrown weapon" which I think may not be intended. This might be clarified before an official version of that thrown weapon fighting style comes out or force an errata for the duelist. I would think that they should not stack.
3. Spears vs. Tridents have been discussed at length.
4. The DM assigns damage types to new effects. If your DM allows you to conjure a barrage of nets, then he gets to decide its damage type. As an aside, since the damage comes from a spell, it is magical, and since the conjure barrage spell is based on weapon damage types, I would imagine it has to be either piercing, slashing, or bludgeoning to begin with (most obviously bludgeoning). There are (currently) no monsters immune or resistant to magical bludgeoning, so there would be no mechanical difference.

Treants are resistant to magical bludgeoning and piercing damage. But yeah, the exact confluence of circumstances required to make the whole thing mechanically relevant will almost surely not happen unless specifically planned to.

well then i have simply not been aware of the discussion previously. I basically agree with you on points one and two, the duelist fighting style is probably not supposed to work with thrown weapons.

But then you said "There are (currently) no monsters immune or resistant to magical bludgeoning, so there would be no mechanical difference." and that is just completely wrong my friend, while you would be mistaken for thinking that most or all creatures who have resistance to bludgeoning is overcome by magical weapons, creatures like wraiths and the tarrasque come to mind, there are in fact monsters who are immune to bludgeoning damage in all its forms, notably all swarm creatures resist bludgeoning, piercing and slashing damage, all creatures whom are basically walking trees like the wood woad, treant and awakened tree have resistance to all bludgeoning and piercing damage (but not slashing damage for obious reasons) and from the tortle package they introduced an strange 2ft tall undead with an sponge like body and a heart that is just an living venomous snake that resists all bludgeoning damage (regardless of if you are using magic weapons or not) but does not resist piercing and slashing

I only looked at immunities. Yes, there are some creatures resistant to magical bludgeoning (some plants, swarms, and one undead). No, there aren't any immune to it.

But the real point of that is that the DM can decide the type if it is going to matter, and when it doesn't matter then it doesn't matter.

There is a rather lengthy post on the trident that I was thinking of when I mentioned it.

A weapon with the light designation isn’t necessarily because of any reason other than the fact that it is light.

Doesn't the Hand Crossbow being a light weapon still take effect, specifically with the Crossbow Expert feat? It mentions that, after making an attack with a one-handed weapon, you can make a bonus action attack with a loaded hand crossbow. So theoretically you could dual-wield a shortsword and hand crossbow, correct?

You can have a sword in one hand and a hand crossbow in the other, however:

• Two-Weapon Fighting specifies melee weapons though.
• The Two-Weapon Fighting fighting style refers specifically to Two-Weapon Fighting (which specifies melee weapons).
• The first bullet point of the Duel Wielder feat also specifies melee weapons.
• The second bullet point refers to Two-Weapon Fighting (which specifies melee weapons).
• Only the third bullet point of the feat about drawing two weapons would apply to the hand crossbow.

Quote from TransmorpherDDS >>

Doesn't the Hand Crossbow being a light weapon still take effect, specifically with the Crossbow Expert feat? It mentions that, after making an attack with a one-handed weapon, you can make a bonus action attack with a loaded hand crossbow. So theoretically you could dual-wield a shortsword and hand crossbow, correct?

Crossbow Expert does allow that but the feat only allows you to ignore the loading property - not the ammunition property. So once you've fired the hand crossbow - you'd need to sheathe or drop the sword to reload it - since the ammunition property requires a free hand to reload.

The Crossbow Expert feat also doesn't mention either weapon having to be light.

If you enchant the bolt case with Swift Quiver it gets around the loading property.

Quote from IamSposta >>

If you enchant the bolt case with Swift Quiver it gets around the loading property.

The Artificer's Repeating Shot infusion is probably a much easier approach.

Only if there are any Artificers around.

Well - I did say probably. I mean 2 levels of Artificer are easier to get than 17 in Ranger unless the setting prohibits it.

Yeah, but maybe you could buy one from an NPC, or loot one from a villain’s corpse. That should only be a Rare magic item.

Quote from Emmber >>

Well - I did say probably. I mean 2 levels of Artificer are easier to get than 17 in Ranger unless the setting prohibits it.

 Or 10 levels in bard.

Yeah, 5e weapons are a head scratcher sometimes. There is also the shortsword scimitar thing. The shortsword is cheaper, lighter, and more classes/races get proficiency in it, but the only difference is damage type.

My own observation about weapons is that a special case for two weapon fighting should be considered for a Rapier and Dagger combo.  I understand this is the classic manner for fighting with two weapons.  I respect the light weapons concept.  It seems strange that a fighter would engage with two longswords, for example.  Two daggers, two shortswords (possibly) or a Rapier and a Dagger sound like the right options to me.  Actually I would go so far as to say anything (not two handed) and dagger would be OK.  I understand there are other light weapons (scimitars, for example), but Rapier and Dagger would be a proper exception, in my view.

Actually, in general, I'm kinda old school about weapon proficiency.  I think weapon proficiency would be better if limited substantially from the current rules.  Simple Weapons as a general proficiency is a bit open ended, and Martial Weapons is too, for much the same reason.  It is a "thing" to know how to fight with a sword, or a quarterstaff, or to shoot a bow.  A general simple weapons allows just about something from everything.  And the Martial weapons has the same approach.  I would have classes of weapons like Swords, Bludgeoning weapons, Pole Arms, Bows, Crossbows, as weapon classes for proficiency.  Then I would have two weapon fighting a proficiency, but you have to name both weapons.  Rapier and Dagger would be a different proficiency than Arming Sword and Dagger.  But that is why the rules make clear each DM is permitted to modify the rules for their game.  Just remember to make it clear in Session Zero before someone gets to level 4 and asks for the Feat you won't allow.

Quote from MusicScout >>

My own observation about weapons is that a special case for two weapon fighting should be considered for a Rapier and Dagger combo.  I understand this is the classic manner for fighting with two weapons.  I respect the light weapons concept.  It seems strange that a fighter would engage with two longswords, for example.  Two daggers, two shortswords (possibly) or a Rapier and a Dagger sound like the right options to me.  Actually I would go so far as to say anything (not two handed) and dagger would be OK.  I understand there are other light weapons (scimitars, for example), but Rapier and Dagger would be a proper exception, in my view.

 That’s why I wrote this for my campaigns. 

Quote from IamSposta >>

Quote from MusicScout >>

My own observation about weapons is that a special case for two weapon fighting should be considered for a Rapier and Dagger combo.  I understand this is the classic manner for fighting with two weapons.  I respect the light weapons concept.  It seems strange that a fighter would engage with two longswords, for example.  Two daggers, two shortswords (possibly) or a Rapier and a Dagger sound like the right options to me.  Actually I would go so far as to say anything (not two handed) and dagger would be OK.  I understand there are other light weapons (scimitars, for example), but Rapier and Dagger would be a proper exception, in my view.

 That’s why I wrote this for my campaigns. 

 *main gauche, not gouche, or am I mistaken?

Gorram terrible spelling will be the bane of my existence. Thank you.