What would you think of something like that instead: https://gitlab.winehq.org/rbernon/wine/-/commits/wip/virtual-desktop?
I'm not 100% sure about using the per-monitor DPI for that, but I also don't know much about DPI at all, and it seems to be almost a perfect fit and seems to be working alright for your needs. In any case, this is only a minor implementation detail and we could expose the virtual mode scaling a different way if we don't want to mess with DPI.