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.
I don't think Valve wants to be at the mercy of Microsoft and their policy & technical decisions.
By supporting Proton, they are guaranteeing that modern and retro Windows games will be playable on Linux far into the future. Trying to get the next Call of Duty to support Linux natively is, quite literally, a waste of everyone's time that could possibly be involved in the process. I cannot see a single salient reason why Linux users would want developers to release a proprietary, undersupported and easily broken native build when translation can be updated and modified to support practically any runtime.
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.
Making SteamDeck use windows wouldn't impact prices much, Microsoft is really friendly for putting windows by OEMs. Could even run modified to act like current steam deck.
Instead, SteamDeck is there to drive up testing on Proton or straight forward porting to Linux, which just availability on Linux and the previous steam machine didn't drive up
The steam deck is 100% usable without leaving 'game mode' even a single time. Something that is genuinely impossible using Windows as a base. That's the important part
Also when it comes to breaking proton support (Which does happen) Valve + GloriousEggroll give you access to plenty of older and special versions. Surely that's better than rolling back entire software?
My game doesn't work -> I go to protonDB -> Users saying use X Proton Version or Y ProtonGE version -> I switch the layer used in steam
Hard to imagine a simpler process than that
- CD Projekt Red: released Witcher 2 on Linux, didn't for Witcher 3.
- iD Software: released Doom 3 on Linux, didn't for Doom (2016) or Doom Eternal.
- Epic Games: released Unreal Tournament 2004 on Linux, but didn't for Unreal Tournament 3 or Fortnite. (A Linux port was being worked on for UT3, but it ended up getting cancelled.)
- Larian Studios: released Linux version of Divinity: Original Sin, didn't for Divinity: Original Sin 2 or Baldur's Gate 3
Many studios over the years have made native Linux versions, and many studios stopped because the cost of porting exceeded the revenue it generated. Proton didn't exist when Unreal Tournament 3, Witcher 3, Doom (2016), or Divinity: Original Sin 2 released, so Proton wasn't the reason those studios stopped developing Linux titles -- they stopped because it made no financial sense to continue to make them.
Now, with Proton, 79% of the top 1000 games on Steam are gold or platinum rated on ProtonDB. If you're fine with minor issues, 88% are silver rated or better. For the Steam Deck in particular, there are 5,500 verified games, and 16,526 verified or playable games. So I'd argue Proton is doing quite a lot for people gaming on GNU/Linux machines, since they now have access to a solid majority of the top 1000 games on Steam, both on a Linux desktop and on a handheld.
If future versions of Proton break compatibility with older Windows apps, you can use different old versions of Proton for individual games. Steam makes this very easy on Linux, but rarely is it necessary.
I don't foresee many Linux distros breaking compatibility with Wine, which is good, as some devs argue Win32 is the only stable ABI on Linux. [1]
I don't foresee legal issues either, as Wine has been around for 31 years, and its corporate sponsors have included Google in the past. I've seen no indication that the project is on shaky legal grounds.
Microsoft could always create a new API that Wine doesn't yet support, but good luck getting developers to use it -- they've tried many times, but not much has stuck, and most devs just stick with Win32. [2]
1. https://blog.hiler.eu/win32-the-only-stable-abi/
2. >>36060678
We aren't in the 90s anymore. Win32 has stalled, Microsoft has a regulatory gun to their head and Wine's compatibility (at least in the domain of games) is extremely good, good enough to allow for a commercial product to be a success while being entirely reliant on it. In what way is any of this comparable to what happened with OS/2 outside of "it runs Windows applications"?