Next, (in a second step) I was wondering if a uninstall registery
could not be a good thing to have,
to store a record of the installed files so there's no need to keep
the source for uninstallation.
This would required a new command, (and a detailed specification of course)

pip writes an installation record in Package.egg-info/installed-files.txt (based on the setuptools --record option, with filenames made relative). So... that's similar to it. Of course, to be accurate you have to make sure you don't install over those files. So pip should really be uninstalling before installing something new, and probably be fancy about the whole thing (maybe like Enstaller is doing).

But if tools do respect the integrity of those files, it's a reasonably simple record. Well, that and they should be careful about one package overwriting another packages file (which I haven't really seen happen, but of course it *could* happen).