That's why I'm hoping we eventually get a handheld Steam machine once Linux / Proton support matures a bit more.
It's funny you should mention that since I was thinking GamerOS would go great with this if the controller/keyboard get sufficient mainline support. For anyone who isn't aware, GamerOS is basically what Steam OS was supposed to be- it uses Steam's big-picture mode and has a lot of nice quality-of-life features to make it a set-and-forget console-like experience. It also has support for some extra stuff so you can launch non-Steam games and applications from BPM with just your gamepad.
With how strong Proton's support already is, I imagine many buyers wouldn't mind them shipping it with Linux and giving instructions for how to install Windows to get the price down. After all, a lot of the people in GPD's audience tinker with the software extensively after the fact, having to install Windows wouldn't be a stretch. Or, perhaps more ideally, they could just sell it at a discount if you choose a Linux or no OS option.
In any case, with that 1 TB storage, a dual-boot would actually be feasible, then you could play games that perform better on Linux there. With DXVK yielding some surprising performance gains even in some D3D11 titles, not to mention the giant leaps in D3D9 games, I imagine that would be desirable on more constrained hardware such as this. Stuff like Nier Automata's Mesa performance vs. Windows springs to mind.