Is it possible to output the video from a DMG-01 and a GBA to a third party screen like an LCD or OLED? I'm thinking along the lines of using the the system guts and putting them into a larger case with bigger screen, and maybe arcade size buttons.

Best off using a GameCube with a Gameboy Player or a Super Gameboy for the SNES. Currently, there are few devices for the GBA still floating around, and TV-out from GBC and earlier models doesn't seem possible with third party hardware.

Not yet. Sit tight.

http://hdmiboy.com/ there is this, but it's not cheap!

I wish they'd make an RCA boy instead. If they have to make one for gameboy, why the heck would they not make one for SNES and use a super gameboy? I mean, is it not just a tad ridiculous to have that huge thing in your gameboy, with a long controller sticking out? It's like they can't decide whether they want it to be a console or a portable.

Didn't NeX make a gameboy to VGA hack a while back?