Alec,
If upstream wants to fix this problem, they could just make their next release
version 9000, with the one after that either being 9001 or 9000.1.
Or, possibly, they could encourage everyone to uninstall the PPA package
before installing an official one. For example, release a new package to their
PPA that displays a message encouraging everyone to uninstall the PPA package,
remove the PPA from their list of repositories, and *then* install the official
one.
As a general rule, I wouldn’t expect a user to keep a PPA package installed
when switching to an official package. There is generally no guarantee that
upgrading from a PPA package to an official one will work without errors.
Or, once the official package had entered the system, they could instruct users
to remove the PPA from their list of repositories and then perform a
downgrade.
All of that being said, Debian could use an epoch to fix the problem. Having
an epoch on a package isn’t the worst thing that has ever happened.