While I do have a soft spot for this kind of low-level optimizations, I wonder how relevant it will end up in the real world.

The 16% reduction in runtime only occurs because the runtime of the program is completely dominated by the call-overhead of the function (which would usually be prevented by inlining). Polymorphism, on the other hand, makes inlining harder, so it could be relevant for programs with interfaces that have one-liner implementations. Though Go could even overcome that, as all implementations of an interface are "seen" by the compiler.

In any case, this feature could be used to reduce the aggressiveness of inlining moderately small functions, giving us (marginally) smaller binary sizes and (maybe?) reduced compile times...