Your idea is somewhat possible, but it's never going to happen in reality. I can already run windows in a VM for the exact same result.
Running Windows in a VM would be less efficient than running a stripped down Linux stack inside of a container. Going the Linux+Wine route requires less proprietary code and would be free to license. Hardly an exact same result.
Valve are financially incentivized to get as many games working as possible, I don't think it makes sense for them to do nothing at all about this. They have a head start now due to the general crappiness of Windows on a handheld but Microsoft's mobile offerings could catch up and given that would have Call of Duty among a lot of other heavy hitters available while Deck wouldn't, that is a problem that Valve would need to solve in order to not get stomped.