https://steamcommunity.com/games/221410/announcements/detail/1475356649450732547
That feature might be the closest to "Request Steam Play Compatibility"
You can even filter your wishlist to only show Linux games, so you could just wishlist away, and then filter out the Windows games in the wishlist.
However: this breaks one of the intended usecases for a wishlist: indicating to others what games you would like to get as gifts. So this system isn't perfect as of yet.
I also found this, on the steam-for-linux tracker: ValveSoftware/steam-for-linux/issues/447
Hello @ShannonVanWagner, this is a feature request for the Steam Store rather than Proton itself, so I've transferred this issue to https://github.com/ValveSoftware/steam-for-linux/issues/5809.
Feature Request
I confirm:
contain this feature already.
Description: Please add a "Request Steam Play" compatibility button to all games in the store. This way I could quickly indicate to the game maker that if they could make it work with Steam Play, I might be willing to buy it. As a bonus, could also add a "Notify me when this game works in Steam Play" option.. I'd surely use it.
Justification [optional] Just want to repeatedly buy some more good games that will work on my Linux machine.