Tarek’s reply on IRC:

> I think we should make it dumb: in case of a conflict, it's always
> better/simpler to let the user deal with it.  A simple "could not
> install because you have package X version Y installed'.  Trying to do
> something smarter is very very hard and will probably fail.

About adding smarts to deal with simple cases like the one you mentioned in your email:
> If we provide automation for simple cases, people will want more.

So I think we’re leaning towards rejecting this.  pysetup is a simple installer for simple installs; pip and other installers will use the information returned by packaging.depgraph/install to be smart about conflicts.