Aw dang, I missed the start of this thread on account of being asleep... Sorry. Here's my two cents.
First, I want to chime in with everybody who supported ability retention, mostly because this downgrading/stylistic shift stuff seems to take some of the fun out of the whole thing. I mean, if a caveman can't get transported into a cyberpunk metropolis and wander around hilariously drunk, attacking people with a club, then what's the point? I get there is a point, but it's a smaller point than it would otherwise be.
Another thing. Do we assume everybody everywhere speaks the same language? For the purpose of not overcomplicating everything, I suggest we make it so, though at the player's discretion, they can have an accent relative to the language of another world.
Thing number three. The "central hub" idea sounds sort of useful to me. Suppose a player in World X finds a gateway into World Y. Yay. GM X PM's GM Y (wow, so many capital letters), but it turns out GM Y is temporarily unavailiable. Then GM X either can't continue his game until GM Y responds to his PM, or is forced to make the player wait outside any game at all, which is mean-ish, or has to say that whatever portal the player found is not functioning currently. Or the player can be transferred to the hub, where they can screw around until their train arrives (Whoa. Interdimensional train station!). The last option seems preferrable.