I've been thinking of this a bit lately. I'm not going to do it cos I'm not THAT interested in it, but it's interesting all the same.
Lots of people who don't have the space or $$$ for a full-size cab build a standalone controller. Why not mount a little motherboard (I'm thinking a shuttle N-force2 board since it's small, but not crippled like those mini-ITX boards -- good video, great sound) inside the control panel and instead of having just one cord coming out the back (USB) you could have two or three (Power, S-Video -- USB maybe so you could hook up gamepads or something). All you'd need is enough space for the Motherboard, a hard drive, and a little power supply. I believe that most two player panels have plenty of room for this.
It would become a completely enclosed Mame console that could quickly hook up to any TV. Take that Nintendo! Speakers could even be mounted inside the panel. Or you could have outputs on it.