I think package owners have a responsibility to be contactable, but that the time-frames should be long to allow for the fact people do go off the grid for valid reasons sometimes. I'd suggest something like 2 months is a reasonable interval to allow; if contact via email and available social media fail after 2 months, then broken packages without evidence of maintenance in the source repository should be moveable.
Inactive, abandoned and nonfunctional packages could be defined as:
-- Owner uncontactable via email or social media for 2 months
-- No alternative representative for the package identified
-- No evidence of maintenance in the source repository for 1 year (?)
-- Package is not installable via pip install on 2.7 or 3.x
This is as distinct from the squatter clause, which is really about never-even-started, never-did-anything registrations.
If the original owner wants to keep the name, then I think they get to keep it regardless of the requesting parties desire to get a hold of it.
Onus should be on the requesting party to supply evidence of the criteria via the issue tracker.
Making things too complex? Maybe...