Not got anything to particularly hand. It's mostly offhand articles and pub discussions (drunken freeform thinking is remarkably common and useful in physicists, let alone with undergrads). By its nature, it is into the realm of philosophy, rather than science. It is untestable, since there couldn't be any communication with other bubbles.

As for the time flow, it's fairly arbitrary. We perceive ourselves moving through time via indirect means. Those are potentially an illusion, even in our bubble. The rate of entropy, or the speed of light could be vastly different. That would change the perceived "speed of time" (whatever that means!) compared to some arbitrary communal rest frame.

The big issue is that we don't currently understand our own space-time. Speculating on over variances is very much "how many angels can dance on the head of a pin".

If you want something a little more scientific, cosmic bubble theory is the current version of the theory.

Oh, and the same base assumptions basically preclude FTL. In a relativistic universe, FTL is time travel, with all the resultant problems (tachyonic anti-telephone being just the most obvious)