I emphatize with your situation and it's a great example. As crazy as this may sound, I think you would have to build every possible permutation of your library

I emphatize with your situation and it's a great example. As crazy as this may sound, I think you would have to build every possible permutation of your library and make all of them available on pypi. You'd need a some new mechanism based on metadata to represent all the options and figure out how to resolve against available system libraries. Especially that last part seems very complicated. But I do think it's possible.