Maybe the GPL people need to get with the times, then. LLVM exists largely because the GCC people were so obstinate. I'm a big believer in copyleft software, but it only works if people want to use your software with their projects.
LLVM was always trying to pitch itself as a whole-lifetime optimization system. In practice, this meant focusing on LTO and PGO compilation modes. The idea of runtime or idle-time optimization were always kind of a next-todo step rather than anything actually implemented.