I agree. At the end of the day, C++ headers are quadratic. Folks who don't respect that fact are going to end up with files that take minutes to build. Threads won't save them. Linearly increasing core usage can't satisfactorily address an exponential problem. It would also mean make -j#cores may need to be adjusted to make -j#cores/#threads to ensure the system doesn't get bombed if a bunch of boost-heavy files get scheduled for compilation at the same time.
If GCC devs try anyway and end up adding mutexes to all their data structures, it could potentially make things slower for everyone. It'd be overkill too. Last time I checked, GCC doesn't even memoize the O(n^2*m) stat system calls it does when processing includes (where m = # of -I / -isystem / -iquote flags). That would be a very simple patch to make things less bad. But it still doesn't solve the problem, which is that programming practices need to change.
If GCC devs try anyway and end up adding mutexes to all their data structures, it could potentially make things slower for everyone. It'd be overkill too. Last time I checked, GCC doesn't even memoize the O(n^2*m) stat system calls it does when processing includes (where m = # of -I / -isystem / -iquote flags). That would be a very simple patch to make things less bad. But it still doesn't solve the problem, which is that programming practices need to change.