It will never happen, but my dream is for the Asahi devs, Valve, and Apple to all get together to build out a cross-platform Proton to emulate and play games built for Windows on both x86 and ARM hardware running Linux.
A Steam Deck with the performance and power efficiency of an M-series ARM chip and the entire library of games that run on Proton is just...dreamy.
The end game for Valve isn't Steam Deck 2 or 3 (which is statistically impossible for Valve to produce), but for Steam to be on everything.
Most of the studios that own those games, and target POSIX like OSes on mobile phones and game consoles, are yet to bother with GNU/Linux versions for SteamOS.
What Valve want is the dissolution between platform/architecture and store. By my eye, it's the driving force of their efforts, more so than them selling hardware or being the open source good guys. Not to undervalue their work in helping make Linux a first class citizen for gaming, but the core of their business model is getting people to engage with their store, full stop, and being able to sell their games on Android (and elsewhere) would massively extend their reach.
This may go both ways too, there's also been indications that Valve have been tinkering with Waydroid, meaning Steam could also become a store for Android-native games.
In order for Microsoft to rug-pull the technology (which is quite different from rug-pulling the business model), they'd have to break compatibility on Windows itself. Video games remain a major reason for home users to run Windows. Making ABI-breaking changes to Win32 or DirectX is just not very likely to happen. And if it did happen, it would be a boon to Valve and not a harm.
The biggest risk (and this would be a classic Microsoft move, to be fair) I can foresee is aggressive API changes that make it hard for Valve/Wine/Proton to keep up but also make it hard for game developers not to. I'm not exactly sure what this would look like, and a lot of the core technologies are pretty stable by now, but it's a possibility. It's not, however, going to harm anything that already exists.