Well I guess that with something as undefinable as "multiple dimensions/universes", any world could be connected to any other world through some atomos-like plot device. That being said, Vana'diel's time-space continuum has got more holes than a swiss cheese nowadays, and I'm not sure how many more dimensional warps it could take without imploding into a singularity.

I've seriously lost count on how many parallel realities and alternate histories there are in Vanadiel. Probably something like 6-7. I always like to think that introducing time/dimension travel to an otherwise "normal" world is one of the surest signs of writers starting to run out of creativity.