

Possibly, but I don’t see Google doing that either. It’s not about where the app comes from really. The thing they are going to restrict is the developer. A developer can not have their app installed on a certified phone, regardless of where the user got the app, if the developer is not registered.
So, since there are no regulations to allow a user to install apps from any chosen developer, only from any chosen app store, there likely will be no regulatory recourse like Apple is facing as mentioned by the OP.
If it’s POSIX compliant then it will work on all versions of Linux/Unix. Otherwise it depends on specific implementations that have branched for decades.