was doing some research for my Atari book and stumbled across these videos of something I thought was both fascinating and incredible feats of engineering and reverse engineering of classic Atari 8-bit hardware been executed by true engineering professionals and due to what seems an incredible amount of effort and possible to produce this, I can't see there been an market or would cost a vast amount of money for the effort, so if your planning anything like this, firstly enjoy your work and secondly don't panic!
I find these projects interesting, but I'm a guy who sees no reason for something made into a portable that wasn't meant to be portable in the first place. If I want a portable Atari to game on, I have my Lynx. If there's an outside chance I'd want to use my 8-bit in a portable way, ever, I just download the Atari emulator for my Android phone. But more power to those who just have to have an Atari 8-bit portable! Or any other vintage computer or console turned into a portable.
I'll just stick with modifying my originals to be used on a desktop. One thing about me though, is I like to play games on big screens, the bigger, the better, like my projector. Even my Lynx I'm planning on doing the mod to it for VGA out so I can use it on a proper monitor, TV or projector! That's why I doubt I'd ever want to use even an emulator on my phone. I tried it for the Lynx once, for about 15 minutes, but couldn't stand the "controller" (and also my hands on the "controller") taking up part of the screen and obscuring the game's graphics. That bit isn't an issue with something like this 800 portable, but like I said, I have my Lynx.
I definitely appreciate the undertaking and aesthetics. I don't think I would like the red button keyboard he uses though, IF I wanted to do a portable like this, I'd actually look into using a membrane keyboard from a ZX81. Obviously a 400 keyboard would be too big, but I bet a ZX81 would fit nicely. At least I'd make the case so it fit nicely, but I don't think it takes up more area than the keyboard he made. Maybe just use the red buttons for the function keys.