Since there isn't a way to do this in any fashion I never really thought about it. I think most people either set the shebang to the version of Python they want it to work with, have pip install the entry point which will also set the entry point, or assume that e.g. python3 is new enough to work.
But even setting a minimum is potentially troublesome if there's an incompatibility, e.g. you used 'async' as a variable name and suddenly you installed Python 3.7. :) So I don't know if the desire/utility of having a minimum is worth the added complexity.