Earlier quoted context omitted.
Face it, your work will never be as immortal as autotools. You also bet on wrong languages. M4 is battle-tested, stood the test of time, and is much more stable.
You are right, and that is an excellent way to state my goals: I hope to create systems that have as much lasting impact as autotools.
Or more precisely, as a result of that monoculture there is a single implementation of build.rs and it cannot interoperate with anything else. If cargo could optionally generate a build.ninja file or some JSON with the command it runs, it would be so much easier.