Hi Stefan:
I'm with you on your thoughts about removing the need for users to often have to deal with byte-code or native-code compilation differences when running different major versions of Emacs. But it is now 2022 and the situation seems to be much worse than it was five years ago. Say you use Emacs 27, 28 and 29, some with native compilation and some not. But you want to keep the same set of packages in use across all these installations. You can set your user package directory so you get different package installs per Emacs version but we don't have a way to synchronize the set so that any missing or removed ones are updated as you move from version to version.
I just wanted to start some conversation on this and get people thinking about how to make this easier on users of multiple Emacs versions. It is also an issue for package developers who want to test their package compatibility across major versions.