> The two major C/C++ compiler vendors (i.e., gcc and llvm) could simply go their own way, with regard to new language features.

They could, for developers that don't care about 80% of the desktop market and one of the major game consoles.

However I am also the opinion that C++26 might be the last standard anyone cares about, outside some language nerds, and that one specifically due to reflection, otherwise I guess many would be happy with C++20 or C++23 as their last standard to care about.