I think it would be interesting to package up ReactOS [1], which shares a lot of code with Wine, as a VM that could be shipped with an application along with something like QEMU. If I'm not mistaken, QEMU supports virtualization through the Windows Hypervisor Platform and macOS's Hypervisor.framework. Could be a good way for GOG to sell old Windows games.
Not to take away from ReactOS as a project, this somehow doesn’t make much sense to me, as WINE (and its spin-offs, like Valve’s Proton) is already good enough as a portable gaming platform.
I was thinking in particular about the Wine on Windows use case. Running ReactOS in a VM seems a more direct route than running Wine in a Linux VM (e.g. via WSL 2).
Edit: I also think it would have made a lot of sense for Valve to invest in getting ReactOS running on their Steam Deck hardware, so they could use that instead of Linux. They're clearly a Windows-first shop, and ReactOS is modeled on NT right down to the kernel. Having a Unix-like OS running underneath, when one really just wants to run Windows code, adds an extra translation layer and impedance mismatches that might even be user-visible.
WINE is Windows APIs running on the Linux kernel ( host OS kernel ). The Linux kernel is already high quality and high performance.
ReactOS is Windows APIs running on the from-scratch ReactOS kernel that is not very good.
The ReactOS project is not the source for most of the APIs a game is going to use. Many of the come from WINE.
Using ReactOS instead of WINE on Linux makes little sense at this point. It would certainly be a lot more expense and time to create a commercial quality product. Most of the work creating API support to WINE / Proton is portable to ReactOS of the kernel ever gets there.
About the ReactOS on Steam Deck bit: I'd suspect that this might be a bit too much for what looks like a fragile peace between Microsoft and Valve. Doing Deck on Linux is one thing (in the days of Linux on Azure it can't be much of a provocation), but ReactOS could still be too much I think. "If you want Windows, ask us for a good offer!" Technically Proton on Linux might be very similar (even the same code in key parts?), but on a subjective level, I could easily see one trigger a red line reaction the other would not.
I actually did that and solved a real problem with it (being able to run the Riven installer on a newer windows), by building Wine under SFU/SUA (I don't know if that still exists or has been removed in favour of WSL) and running it against XMing32. I never got freetype working so all the text was monospace and overflowing the dialogue boxes, but it was enough to run basic programs.
