I don't think any of their stuff doesn't work now. Even stuff like Halo with anticheat has been allowed to work via proton already.
This doesn't provide any promise that you can use gamepass or windows store games on Linux, and it doesn't provide any promise that they don't use anticheat in a restrictive way on Linux machines. They can trivially provide a bypass in the cloud environment that doesn't get shipped to end users.
Hopefully they don't do that, but this doesn't really mean a lot to individuals buying their games.