It's clear that Valve can't convince developers to make Linux ports (Even Doom with Vulkan support doesn't have Linux build that's the shame). So I suggest to allow developers to add purchase option called "Crowdfund Linux port". Let the developer decide how much money is needed.
Current approach doesn't work. Linux ports suck and lots of people cry about Linux version of favorite games. Let us vote with our wallets. I would gladly support games just to play them on my favorite OS.

This will ensure developers that they're not wasting time porting. Let community help make Linux gaming platform