Well, think of the possibilities! With the creation of a set of standards, you could make a set of ROMs able to trade back and fourth between all four generations! It would change the way people hack pokemon games.
EDIT: So, I have given this some thought and I'm wondering if your thoughts parallel mine. In theory, to bridge the trading gap, so to speak, all you would really have to do is make a generation II game, say crystal, compatible with a generation II or IV game. Most likely III, i think, considering if you could figure out how to make this work on a retail cart, the two generations could be hooked together via game link cable. this would basically open up the playing field in regards to pokemon availability and replayability. I'm surprised Nintendo hasn't tapped this goldmine resource themselves. So, what exactly are your thoughts on implementing this?