Hey Ben, I know it hasn't been too long since the last portable you made (ZX Spectrum), however I was kind of waxing nostalgic since the recent birth of my son. When I was a little tyke one of the portable systems I owned was a Sega Nomad. A system I loved due to its ability to play on a television as well as a standard Model 1 Genesis. I know that they can now a days cost anything from $85 to upwards of $300 pending condition. Regardless I think the concept I wish to suggest would be a brilliant one. I've seen modded Nomads with updated LCD screens but that is nothing. You are Ben Heck after all. I have a list of bulletpoints of what I would wish to see in such a redesign.
-First and foremost fix the horrendous battery issues. I had gotten the official rechargeable battery for mine but I'm thinking this one could do with a more contemporary lithium-ion rechargeable built in.
-Secondly perform a screen replacement with something of an easier to look at scale. Perhaps something along the lines of a common LCD used with GPS systems in scale as opposed to the classic sized one as well as upgrading the audio format to the system having on board stereo with better speakers.
-Next updating the TV connection to an HDMI set up using a mini HDMI port in the system. (This mod is possible as it has been done to a Model 1 Genesis and to my knowledge the visual output capacity between the Nomad and the Model 1 is 1:1 I could be mistaken however)
-Also I think it would be important to make it to where it has the option of another controller port if being used in lieu of a standard Genesis rather than using the system itself as the controller, perhaps by use of an on board toggle for the Player 1 slot.
-Then last but not least, re-design the shell of the system to be more ergonomic and look closer to something Genesis related. Perhaps for example looking like an actual controller merged with the cartridge port area of a Model 1 in concept. Perhaps even something that more easily hides the cartridge slot from view.
I hope this piques your interest. I look forward to this being a possibility.