That function is currently only used to find the wheels that are temporarily added to sys.path to bootstrap the "pip install" invocation that actually does the install. I'd prefer to leave that as it is, because using the known-good bundled versions in preference to user-supplied versions seems sensible.

What's actually installed is determined by pip's logic, so this bug report is no longer relevant once the wheel patch goes in. (Assuming pip handles the scenario described - if it doesn't that would be a pip bug, though).