I came across this interesting bit of news.
Innex Readying Sega Nomad Successor
My girlfriend has a few Genesis cartridges laying about and I was looking into buying a Nomad via Ebay. I may buy a Retro Gen instead, although I view the lack of a second controller port to be a limitation.

then just buy a sega genesis knock off, seriously they're pretty cheap
http://www.amazon.com/Station-System-Nintendo-Genesis-16-bit/dp/B00117GOWE/ref=sr_1_9?ie=UTF8&s=miscellaneous&qid=1247719708&sr=8-9
that's what I did for my supernes.

Umm... that's what he's talking about. Except it's not a Genesis knock off it's a Nomad knock off.

I've got a bag full of MD/G carts next to me. This may cause them to be dusted off and used again.
Also, I need to fix my Game Gear to use all the MS/GG carts.

he's talking about a 2nd controller port.

Considering he was originally looking at the Nomad and not the Genesis or CDX, I figured portability was more important.