The idea is interesting. However, worth noting that you would have to increment main() with literally every change, because when you fix a bug in foo#10 (by rewriting as foo#11), you'll need to update the affected call sites to use foo#11 instead, which means they get incremented, too, so you need to do the same to their callers, all the way up to main.
You'd absolutely need tooling to automate some of this (present a list of call sites; you select which should use the new function). It would also increase the size of your code base by a lot, although I'm not sure that's as much of a problem since we may be spending less time reading code and more just writing a new function.
You'd absolutely need tooling to automate some of this (present a list of call sites; you select which should use the new function). It would also increase the size of your code base by a lot, although I'm not sure that's as much of a problem since we may be spending less time reading code and more just writing a new function.