People are talking about doing various ports of AR... Well here are a few things to consider:
GamePark32 - www.gp32x.com www.gamepark.co.kr a Korean company makes this Gameboy Advance sized (not the new thin one) game player that's actually an emulator!!! No keyboard, but if you can map commands to the buttons, it will emulate an atari 8 bit, and about 2 dozen other things.
Tapwave Zodiac - www.tapwave.com - this month's Game Informer has a picture of the Tapwave Zodiac, a Palm OS based game system, again around the size & shape of a Gameboy Advance. The development platform will be open, perhaps even open source - so if you do plan a Palm port, this is something you'll want to keep in mind.
If you want to start developing now, being one of the first tapwave games available may even help you build a name for yourself and perhaps you can start a gaming company around it.... But with a ship date in October, you'd really have to get your act together.