"pip install --user -r requirements.txt" is not a terribly odious "installation checklist", and I don't think it's the start of a slippery slope towards one either.

If you're worried about people not RTFM when using your projects, you could always start your scripts with the standard try/import/except wrapper around the required package, and tell them to run pip install when it's not found--or (and this is a terrible idea) run it in a subprocess for them.