my theory is that the roman numerals will become too long and unappealing, XIII would be shaky if it weren't for Red XIII to make it look cool. then they'll get away with it going back to 3 digits, XIV, XV, XVI, but stuff like XVII is really up there. i think SquareWatever will start displaying the numbers in a different way.
Final Fantasy Zero = an idea of mine, it's neat no?