Don Miguel tells me work is going on on one. And things don't get traded on GP32, they get ported. There's a very very very big difference. Trading suggests there's only one, for a start. And that they already exist.
So far as I understand, any emu that could run on a 133MHz Pentium that was running DOS and had 8mb of ram would probably run on a GP32, so its only a matter of time.