I think you are the one not understanding. All those things you are thinking are issues are not issues. Let me repeat it to you: they are already in game, NPCs use it. It's not a design choice, it's an arbitrary restriction. If it was an art style or whatever then there would be no bubbles at all. Go ahead to some of the NPCs in Limsa Lominsa and stick your camera as close to their chat bubbles as you can and you will see how the game handles most of those things you are asking. What's more, you can go right now to other mainstream MMOs and see that they have solved all those questions you are throwing as if they proved how hard and time consuming it is. Even if they added it at a later date. It doesn't matter. They have them and it doesn't affect their performance at all. Just make it so we can deactivate in the options and make them deactivated by default, if you are so worried it's going to freak out the game.
For example, deciding how far you render the chat bubbles is NO different than deciding how far you render a BLM's AoE spell or how far you render the floating name above them. I would say it's even less, because the text flying on top of our heads or coming out of mobs that we are attacking is near constant, and AoE's and skills have a lot of MOVING textures and polygons. Have you ever chatted with someone in game? Unless they are using a program or spamming messages by using the arrow key or copy-pasting, there's no physical way they can type text as fast as my archer deals damage. And you can solve that with anti-spamming measures that hopefully the game already will have included.
All those things you are thinking are issues are not issues. Other games have solved it, Squee clearly has solved it (because their NPCs use them). There's no reason not to implement them unless Squee has an ancient vodoo curse that will crows to come and eat their eyeballs if they implement them for Player Characters.