i didn't know vagrant story was in Ivalice...how very ignorant of me
anywho, i don't think Square would consider that, i suppose it would depend on how well recieved this game is, plus there aren't as many (good) characters in those few games ^^ I honestly don't think they would ever consider something like that.
as for the Ivalice alliance thing, i was led to believe that it was only The Lion War, FF XII and FFT: A2 involved with that...but on second thought i supposed revenant wings, etc. would be in there too, so i'm not sure, i think at this point they've really done enough with Ivalice and it would be overkill to do any more, at least in the near future...