I wouldn't get my hopes up, ever. Apple doesn't support the pipeline required to get Proton functioning on iOS, and when Apple stopped supporting non-Metal APIs, Valve stopped supporting Proton on Mac. Unless Apple unlocks iOS bootloaders or changes their policy concerning Khronos APIs, you will be enjoying this on Chromebooks, Android handsets and Linux clients only.

It would be cool if this was ever going to happen, but you have to remember that one of Apple's largest revenue streams is their captive audience of microtransaction-addled users. They aren't going to make things easy for Valve even if they're forced to open up.