It's not going to happen for many different reasons. Nat Brown who has worked for Microsoft on Xbox, Valve and until recently at Apple as a Metal engineer has said in interviews that neither Valve nor Apple are interested in a solution like integrating GPTK in Steam. Apple wants native games.

He has started working on his own solution Kaon but it’s far from complete. You can find it at https://github.com/natbro/kaon. Here is a 2 hour long interview with him by MacGameCast: https://youtu.be/JPKkMYd5NcM?si=RLEciObYdEg30Uhs

There is also always Heroic launcher. You can download and use Wine and GPTK with it and play your Steam, GOG and Epic games.

Apple has pretty much done everything possible to hurt their gaming scene and it doesn't look like that trend is ending anytime soon.

Proton relies on Vulkan which Apple flatout refuses to support, Valve has little incentive to invest writing a whole new compatibility layer + emulator for such a demographic, and Apple wants everything from this point on native which would be great if there were a big market for such a thing.

Who knows what what gaming will look like in 5~10 years but for now Mac gaming is doing pretty poorly and only Apple is to blame which oddly enough seems to be the last entity Mac gamers want to blame.