You'll still see those though? A fully GPL implementation doesn't prevent the current implementation from being used in a proprietary rust distribution... unless of course the GPL implementation were to fork from the current implementation... which is the main thing people against the GPL implementation are worried about

I think, the GCCRS project takes the rustc implementation as reference, and targets 100% compatibility with them as a fundamental goal and requirement. There is no schism involved.

C++ and Java, which have many implementations, also have proprietary distributions, see Apple’s fork of Clang, Microsoft’s MSVC, Azul VM, Jamaica VM, ...

And some of them are pretty nice. Life is good.

When you don’t have a GPL implementation, the only good implementation might be closed source fork of the LLVM version, effectively forking Rust into Rust and Rustium. Will life be good then?

This seems like an astoundingly remote possibility.

Given the companies backing LLVM and the surrounding ecosystem, I think it’s an astounding possibility.

Companies love permissive licenses for a reason.