I think you're being extremely vague about the things you are using your GDP for. Nothing you've written strikes me as something that couldn't be achieved with a proper I/O module attached to a smartphone.
The most limiting bit about phones is the OS itself. You could hypothetically get most of these things working on phone OSes, but only for a massive amount of effort to port something for a single-digit number of users. I don't even know how you'd get a compiler going, but I suspect it would be a non-starter on iOS.
> Smartphones have their on OSes, UX, applications, etc. The point of projects like GPD Win or the one linked above is to run the same programs, OS, etc as you'd run on a regular laptop or a desktop PC.
Sure, an Android device could probably be hacked to do that. But most Android devices are usually locked-down, whereas the GDP & friends make it a point to be open.
I guess we should probably push for more openness from smartphone vendors (including Apple) instead of having yet another different device. Especially since now everything and the kitchen sink connects via USB-C. I'd absolutely love to be able to plug my phone in the USB-C dock at work instead of lugging around a laptop (which I use on top of a desk tethered to some fat screen and external keyboard like 99% of the time anyway).
At one point, I remember Samsung had something like that on their Galaxy line (DEX? can't remember the name). I was actually ready to pull the trigger on a tablet with that feature. Luckily, I found out they had just or were about to remove it.
You could, in theory, use a smartphone for this but the software situation is so terrible that you really can't.