> As an alternative, virtualenv could be changed to create a pyvenv.cfg file with the interpreter version like pyvenv does. Seems pretty simple and unproblematic to me and it might actually be useful to know the interpreter version without running it in other places besides the launcher. What do the pypa devs think about this?

As one of the pypa devs, I'm in favour of this. I'll probably
implement it in due course, time permitting. But of course, a PR from
someone else would be a help :-)