I've heard some people wondering what changes will be made to Suprise in the new edition, based on its mention in both playtest releases.  But I'm wondering if we already have all the rules.  If you are hidden, you have advantage on initiative rolls.  If you are incapacitated, you have disadvantage on initiative.  That might be all there is. 

Surprise in 5e was a simple concept that was hard to explain.  We know there is technically no 'surprise round,' but there often was in actual effect. If one side didn't get to act, move, or react until their next turn, that was basically a surprise round, just on a case by case basis for each individual. The punishment really came when one person was surprised AND also rolled low initiative, meaning they might just stand there for two rounds of attacks and take it. (That's how we got TPKs in the very first encounter in Lost Mines of Phandelver.)

What if the rules for hiding and incapacitation are all there is to it now?  If you have advantage on initiative, you'll probably go first, and get a round of attacks off before the other side does. The real change is only that it won't always work, and that no one gets completely wiped with a bad double turn scenario. I'm pretty okay with that. It doesn't sound bad at all. And it certainly is easier to do. 

Side note, if Assassin works the same, it's a good reason to pick up the Alert feat at level one.  Advantage from hiding, a bonus to initiative, AND the ability to swap with another character if they still rolled better, almost guarantees your ability goes off.

What do y'all think? Is there anything I missed? Is there anything we really need to add to the Surprised rules other than this?

I think you are right and the design is intentional. action economy is too important for one side to get that whole first round free of enemy actions.  It solves multiple problems all at once including the assassin rogue, lair actions on surprise, lopsided combats, "when combat starts" questions ect.  

it seems like a good choice.