It is funny that people think Valve would sell out instead of becoming the big evil.
As Valve continues developing an OS agnostic platform, they start building into various tools that require a Steam account to play games in order to defend their app store. Maybe they buy Unity and make it a Steam exclusive, maybe they make their own engine that can be played on Windows or Linux.
Integrate Chromecast technology to make a console like multimedia device to compete against XBox and PlayStation. Then, start selling video and integrating streaming access.
Push the Steam Store to become bigger. Sure, you aren't forced to use the Steam Store on most Valve developed hardware, but it is default.
Then, like Google did with Android, pull the tech stack from the open source tools to become wholely integrated with Steam Services.
Most of this already exists and they haven't taken that tack, though. SteamOS is just Arch and KDE, with access to anything Arch has access to. If you don't like that, Valve made it trivial to put another OS on the Deck, like Bazzite.
Steam Play is already a streaming technology, which works great and is free to use and has been for like at least a decade.
Steam Store is already gigantic, despite having some well funded competition who has to resort to exclusives and free game giveaways to entice users. It's already the de facto default game store for PC, and provides lots of extra features beyond just game delivery.
Most of the technology Steam uses (like Proton or GameScope or Arch) are open-source. We can (and do) fork their work for our own purposes regularly.
I don't think Valve is perfect, but I do think they value their open approach to technology. I think as long as the company is never publicly traded, I would imagine anyone who currently works at Valve would share that attitude with GabeN, otherwise I imagine they wouldn't work there long.
If they go public and have to report to shareholders, then I completely agree that the enshittification will be swift and merciless. I hope Gabe makes Valve an employee-owned co-op or something when he decides to retire. I can only imagine he has strong plans for the transition of power.
I'm commenting more on how Valve could become evil while maintaining and expanding its markets. Part of that is using open source as a way to reduce development costs while still controlling and monetizing key parts of the tech stack.
You know, as long as their management structure stays relatively similar to what it is, I think I'd be more fine with them being the big evil, compared to basically anyone else.
Edit: and also as long as they stay a private company, that would also be a big concern, but I guess that's maybe the same as saying their management structure stays the same