contributing requires the "admins ... declare code abandoned and the seize it"
I assume I misunderstand you, because this strikes me as disingenuous at best. I would guess that any PAUSE author who requested that their work be taken off CPAN would have their request honored. It may provoke some comment and consternation, but given that an author may have legal issues regarding authorship I see no advantage in CPAN's noncompliance.
I don't believe CPAN contributions require that "admins ... seize code" nor do I believe that the fear of such prevents contributions.
CPAN is a distribution mechanism not a development tool. There is no reason to expect CPAN admins to jump to take on new tasks that have little to do with that for which they volunteered.
When you release on CPAN, you don't have to stop developing the codebase where, how and with whom you like. I should have been clearer about the timing.
There is nothing I see in the rules of the CPAN that you are complaining about; how is CPAN stopping you from setting up a collaborative development process for the modules in your care? You just seem to want CPAN to be something completely different than what it is.
I like what you are proposing, I just don't see it having much to do with CPAN.