Is this really limited to the DSi? I don't really care. For any handheld nintendo console I'd like to see a classic nintendo remote design like they did with the SP.
Or how about one that's a nod to the super famicom controller? Or even a dual-screened game n' watch homage?
I think that first might be a little too plain, and I've never really been comfortable with game and watch. That's just me though, and I've never known what most people would like.