I'm going to assume RenPy here, since that is the most common style of interface for realistic 3DCG + text games...
Wouldn't the thought bubbles have to be presented 1 at a time, so the player has time to read them?
How is a bubble presented near each character any different than the same text appearing at the bottom of the screen? If anything, it could be seen as worse - since the player's eyes would need to roam around the screen looking for the next speech bubble.
Unless you're thinking of multi-panel windows like comics, where all the speech bubbles are already shown and the player can read up to 6 or 8 panels in turn at their own pace - before clicking to continue. In which case, the text might be a bit small in general... but certainly on mobile devices.
Personally, I gave up very early on with clicking the mouse to advance the text. Instead, I set the text speed to appear slowly (slightly faster than my usual reading speed), one character at a time and set the auto-advance timer to be slightly slower than my usual reading speed of long lines - so I can still read each line when my brain is wandering. Then, rather than going into the preferences every time in each game, I created that overrode those settings as the defaults. I copy the file into the game folder before each new game/version I play and so I don't need to worry about messing about. I also add a keybind (alt+PgUp) to toggle auto-advance on and off within games that have disabled the quickbar at the bottom of the screen. If you're fed up with clicking... that's another potential solution for you.
If you're thinking of your own game... if it could be made to work... It could be great... or terrible. It really comes down to how well it works in practice. imo though, one of the reasons RenPy games are so popular is the familiar layout and user experience. New is good. New is also risky.