Realistically I don't see how Valve can avoid this. They want all those games on Steam Deck and the new console. Game devs want KAC. Therefore Valve can either provide them with some way to implement KAC - which effectively requires a "signed kernel / drivers only", same as on Windows - or tell them to go away. Why would they do the latter?

Mind you, it doesn't mean that the Linux kernel will be "infected for everyone". It means that we'll see the desktop Linux ecosystem forking into the "secure" Linux which you don't actually have full control of but which you need to run any app that demands a "secure" environment (it'll start with KAC but inevitably progress to other kinds of DRM such as video streaming etc). Or you can run Linux that you actually control, but then you're missing on all those things. Similar to the current situation with mainline Android and its user-empowering forks.