New clone idea: How about a PC-G850VS or PC-E500 clone?

[blackjetrock]

I'm not aware of a service manual for the PCG850VS, but there is one for the PC-E500. Having that and a ROM image would make an emulator fairly straightforward. You could make a PCB to match the original and put whatever processor you want on that, as long as it fits. The display is probably best changed to a modern one, of some technology. Having done this a few times, I have found that finding a display that fits is tricky, and usually there is only one or maybe two to choose from.
Battery life is usually worse, as a CM4 eats power, and the RP2040, which is one of my favourites, is not a low power device in the sense of weeks of running off a small battery.

Another option is to design a case or part case that fits a display and have that printed. having high quality cases printed is now incredibly cheap, and lets you put whatever display will fit in the case.