GCC is almost literally nonexistent as a place for new compiler research in large part thanks to previous stallmanist approaches to managing, this isn't just some cutesy hypothetical about principles and so on.
The above also ignores stallman's manner around people.
I believe that you are referring to the old LLVM modularity? That is old news. GCC is now (reportedly¹) better in C++20 standard compliance, and this will probably not change, since, (reportedly²) both Google and Apple have moved away from LLVM involvement.
When I read papers on new compiler techniques it's never GCC getting the implementation, this saddens me but it's true.
Correction: according to what you've linked, it is not LLVM but clang. This correction would be extremely important for my reply.
I can't see how is that a good news for GCC. This (and other incidents) suggests that both companies have lost interest in investing the future of C++, and they were already building their own languages for a long time. You can argue that they wanted to bend the standard and implementations as they see fit---and it's partly true, otherwise why would you want to join at all---but it's probably more likely that C++ is becoming irrelevant at least in some applications. And if the language is made irrelevant, a better standard compliance means nothing.
LLVM is very much alive at all big tech, to my best knowledge. It's C++ that's dying there (and I say - good riddance).