I can't see the whole 'clutter' thing being an issue, unless you're blessed to be in a incredibly social server. My server Moogle on the otherhand, I don't think chat bubbles are going to be an issue.
Whenever I go to a major city, only a handful of people are publicly speaking, and the majority are sticking to /tell or /partychat.

Whenever the subject of chat bubbles arise, a lot are against it because people are overestimating how big the chat bubbles will be, and how many people in reality actually speak publicly in game. But as others have said, as long as it is a toggle button away, then everyone's happy.