This is great. Proton is getting a lot of testing just based on Steam’s userbase and it is backed by Valve. We also have a lot of data on proton’s performance and potential game-specific fixes in the form of protondb. Making sure that non-Steam launchers can use all that work and information is crucial to guaranteeing the long-term health of linux gaming. Otherwise it is easy to imagine a future where proton is doing great but the other launchers are keep running into problems and are eventually abandoned.
One thing that I am curious is how this handles the AppId. If this AppId is used to figure out which game-specific fixes are needed, then it will have to be known. Do we have a tool/database that figures out the AppId from the game you are launching outside of Steam?