One obvious example of this would be C++, where a smarter frontend that doesn't do textual inclusion of a million lines would significantly improve compile times.
But that's low-hanging fruit "optimization", no? Once you get around it, and this has been forever, the bottleneck is in the backend generation. So if Rust has already solved this, the area where they can improve most is the backend generation?
Most C++ builds I have worked with, and all of them being MMLoC codebases, were actually bottlenecked by the high memory pressure. In part due to heavy templates and symbol visibility.
I think the history of C++ implementations shows that it's not low hanging fruit, it's a huge effort to implement and the payoffs aren't game changing.
