The following paragraph should be added to the packaging guidelines, as it was the source of dispute, despite being common sense:
Packages being merged from a third-party repository, with the intention of getting the package dropped from that third-party repository, MUST use an Epoch which is greater or equal to the one from that third-party repository. This is because otherwise the third-party repository will have to carry the package forever to guarantee upgrade paths for their users.
The following addendum may also be considered (but should get voted on separately):
When submitting a new package, packagers SHOULD check for third-party repositories providing that package and talk to their maintainers if they are interested in a merge. If they are, the above rule applies.