We should make it multiple generations. For a lot of people like myself, challenges can be done on many different generations. They should probably sign up on the sign up sheet last, because they can be placed wherever needed.
I think Karpman's idea of universal games potentially work, but I'd like to try to stay away from that. You can still trade on ROMs with various methods (TGB, VBA link) and no challenge requires you to trade, so I feel that if you want a Pokemon that evolves via trade, you should get the emulator yourself.
As far as later generations (IV and V), if you want to use them and can't find a good ROM for them, but sign up for the challenge anyways, tough cookies. You still have a month to find a good ROM.
I guess the next step here is to determine how many people need to be on the committee.