Are you sure they're gonna open it up to Gen I-IV Pokemon before they release the 3rd iteration of Gen V?
Cause think about this:
You'd end up having
a) Gen I-IV Pokemon who have access to TMs, egg moves, and Move Tutors from previous games.
and
b) Gen V Pokemon who have access to no Move Tutors.
I'm almost thinking they might open it up to the big legendaries (your banned list) for a year, but keep it at only Gen V. There was a year where they allowed thoes Pokemon, but it was a while ago, back when Platinum was new.
If/when a third game in Gen V gets released, it will most likely have some form of move tutor to increase the amount of moves that Gen V Pokemon can know. I wonder if they'd wait for THAT before also allowing in all the previous Pokemon.