Well it shifts the target a bit. Instead of infecting the compiler you'd try to infect one of the core OS components (presumably in the kernel) and have it detect when those were being compiled and insert itself. Probably also infect any compilers you detect while you're at it as well.

This would probably be a bit more difficult to pull off. If someone did pull it off, fully reproducible builds ought to make it readily detectable at least in the absence of some extreme rootkit contortions.