Atari 5200 is huge and at best a candidate for laptop style portable.
I only have one working 7800 and I'd rather not blow it up.
Atari Lynx... duh it's already portable
Coleco Tri-star system... only 4 games??? not worth it (it does have unique triangle shaped carts)
Intellivision II maybe since the main board is about the size of standard NES board and can take plain vanilla power input. Only drawback is the controller is like Colecovision and some games do make heavy use of the number pad, especially my favorite D&D: Cloudy Mountain.
Odyssey^2 would be a problem as some games uses keyboard. Maybe Odyssey^2 laptop with real keyboard not the cheap flat sheet crap.
I would love to have portable Vectrex as its mainboard is small enough. Problem is no one makes vector based LCD display, and it's much harder to build vector to raster converter than it's worth. Might be easier to hack those portable 5" B&W TVs that you can still find for under $30 now.
I'd like to try and make portable TG-16 since Turbo Express is very hard to find and fairly expensive on eBay (plus its small screen is too small for a few games). TG-16's board can be cut almost 1/3 with little problem. And I'd need a Turbo Booster PLUS for the battery backed RAM for storing game saves. As an added bonus if I find the 8 pole double throw switch, I can make portable TG-16 take PCE games without converter
Virtualboy is not really comfortable to hold or mount on head and they can't really be played away from your face. VB is probably the only portable, non-hand held video game system around.
CDi, 3DO, CD32, other lesser non portable systems I have no experience with them so I have no idea what it takes to make them portable.



