It's actually not that difficult to find virtuoso keyboard players. Might be rare in the metal/prog world on Jordan's level I guess, but there are a ton out there that can match if not surpass Jordan in "technical" abilities. Hell, my mother and a couple cousins can play circles around JR and play all his stuff note for note if they wanted. They were classically trained and are concert pianists. Would be tough to fill Jordan's shoes, though. This is mainly due to the mans style and what he brought to the table for DT. His individuality. Thinking of better or less technically proficient keyboard players is irrelevant. Only one JR and no one else in the world is going to procure sounds and music the way he does exactly. Sure, you can replace him, but the music is going to change, regardless of the calibre of player.
In other words, there are a lot of players out there that can match the "abilities" of JR, JP, etc, but no one could ever replace them and have music that would still be identitcal to what we had before whatever change. It would change into another kind of Dream Theater, just as it did when DS joined and then when JR and MM did. Sure, the old songs might be played the same note-for-note, but in a lot of ways with little nuances, they will be different with whoever new you bring to the table.