the elemental planes are important in most DnD campaigns, yet there are no domains that let us be clerics who worship beings in those planes, thanks for coming to my ted talk

My life for warcraft style shaman...

I agree with this wholeheartedly and might do a homebrew about this, but at the moment if you're willing to do a little re-flavoring on official stuff we got this so far;

• Fire - Light/Forge domain
• Lightning - Tempest domain
• Earth - Nature domain for earth (even though nature domain still have the chromatic damages for its divine strike feature).

I agree that there would be elemental clerics, and I would homebrew a whole concept for them if a player asked to play an elemental cleric or if I created a world where elemental magic was significant.  But there would also be arcane magic paths that would be created as well.

If I did this, I would also have to decide if the elemental followers were zealots or just a cult.  If they were zealots, they would seek to destroy followers and temples of the other elements.  If they were cults then they would at least shun the idea of discussing and studying the other elements.  I would also have to create a few legendary figures that were authorities on all elemental magic even though the practice might prevent them from using more than one school; at least they knew quite a bit about each school.

I agree with FallenPhoenix, the easiest way is probably to re-flavor the already existing domains. What is important to remember that cleric domains in 5E aren't restricted to a specific god or deity but rather different aspect of the deities. To use a real-world example, Pallas Athena was both a goddess of war as well as of knowledge and crafting. Thus you could have three clerics, all worshippers of Athena but one is a Forge Cleric, one is a War Cleric and one is a Knowledge cleric.

In the same way, the clerical domains of he people worshipping elemental beings depends on what those elemental being represents. The Fire lord of Learning would would therefor most likely have lots of knowledge clerics.

I mean Tempest cleric is an elemental Cleric already. In my book Nature Clerics have a lot of an elemental Cleric, so does Light cleric(a lot of fire affinity there ). But sure why not creating some even more dedicated subclasses.

Clerics worship god and deities not planes. Questions arise like: "Who do you commune with?" "Who granted you your powers?" "Can you fall out of favor with your deity?"

Quote from dahhahm >>

Clerics worship god and deities not planes. Questions arise like: "Who do you commune with?" "Who granted you your powers?" "Can you fall out of favor with your deity?"

In 5e even though it's very uncommon, but you don't NEED to worship a deity as a cleric (even though the flavor of cleric says otherwise) and can get your powers directly from you belief/devotion. For an example of someone you could be praising, you could be worshiping the ancient primordials/elementals but if you want specific forgotten realms gods, you can easily say that you are a worshiper of the "Deities of Fury" as another example.

Clerics can even just worship a concept like "Order" or "Law" - the Clerics on Ravnica don't have Gods, they worship Ghosts, Order, Law, Nature etc. without a real god.

Quote from leaflesstree >>

The elemental planes are important in most DnD campaigns, yet there are no domains that let us be clerics who worship beings in those planes, thanks for coming to my ted talk

 That's only true if your character is level 5+ and the DM is planning some campaigns with those Elemental planes.

I would say Ravinica's special and hard to take as a canon source rather than a fun source like the Bilgewater or Morty and Rick's setting. The 12 guilds and the guildless are an MTG crossover that gained popularity with the cards (and trust me I know how ridiculous the story of Jace the Living Guildpact or Niv Mizzet is). In the order domain it says the Azorius Senate and Orzhov Syndicate give those powers, but it also says, "On other worlds, gods who grant access to this domain include Bane, Tyr, Majere, Erathis, Pholtus, Wee Jas, Aureon, Maglubiyet, Nuada, Athena, Anubis, Forseti, and Asmodeus."

And then... well, would the same apply for Warlocks as well? That in fact you never need to make a pact with an otherworldly power, and one can simply be given power through... a layer of the Nine Hells, or the air of the Feywilds?

And also, how would you make a clear difference between an elemental Cleric and Druid? To me it seems like the creators already had this conversation, and there was a clear distinction between gaining power by worship of a deity and non-deity sources.

Also, I'm trying not to sound overly defensive or argumentative, but just here to make a few points to help flesh out a world and maybe help ground players to a believably scenario. Cheers for a good discussion!

Would love cleric domains for the elements.

Dedicated elemental themes are heavily neglected in 5e.

Val Hallan, the Norse god of rock.

So I guess "Earth Wind & Fire" were a bunch of multi-classed elemental-cleric/bards. 

Yes.

See 2e and 4e Dungeons & Dragons: Dark Sun Clerics 4 elements and the paraelements too.