Deb -> Rpm?

A basic tenant of good design is separation of policy and mechanism(s).
The mechanisms here are the packaging tools and format used.
The policy is the distribution policy on how to create the package using the tools.

It would allow the packager to learn only one set of packaging tools.
And when the tools are identical, then you can more easily compare the various distributions policy..

As for the users, as I already said, there is no new issue: you can already have a lot a problem if you force the installation of a Suse RPM on a Mandriva distribution for example or if you jump in the stairs, the answer is easy: don't do that.