Let's remember we are not professional artists so a limitation in our knowledge and creativity doesn't affect blizzard's art team's. Not saying Naga will happen, but we cannot determine that they are impossible or not worth the effort.
For me it's more a question of what this ancient engine is capable of. And to what degree I can trust Blizz to not fuck things up.
as to your points,
1. I'll grant you this point although blizzard has almost gone out of their way to make gear look worse on some races than it potentially could (i.e: Pandaren's innecessary belly that looks ridiculous on all things plate)
Well to be fair Pandaren are meant to be funny. Till you piss them off and they kill you with a finger, that is
2. A somewhat different culture (like vanilla night elves), gameplay mechanics (light priest forsaken)
So an ass pull. That's lame, but not without precedent
3. How can gnome warriors titan grip? Blizzard could also give females rather creative weapon holding animations that use all 4 arms.
They could, but I'm not really trusting the engine that much. I will reserve final judgement till I can see it in action.
4.IDK about possible limitations here, maybe you have a point and maybe you don't - this is beyond my knowledge.
It's beyond mine as well as I am no programmer. But since crossbow shots still come out of your chest I sort of gave up on wow animations.
5.Tendrils, fins, faces, skin, possible ornaments (think nightborne), small unique mutations, all come off the top of my head in less than a minute. I am sure blizzard can do better than me.
Let's hope. Although if they can do just as much that's good enough.