In the bytecode every final method would be implemented as an extension function.
Right.
That all said, I am a big supporter of star imports in any case so I don’t really care either way. But I guess that is a different discussion.
I don’t like manually touching imports, I like letting the IDE take care of that 
That would introduce namespace pollution. Imagine you have a file with 20 interfaces and some global methods. Now you import one interface, and suddenly everything is imported.
I’m just talking about the extension methods in the same file as the class/interface imported, not everything in that file.