don't know if this was ever discussed.
Two examples of unused namespaces:
Algorithm::LCS MJD 06-Sep-1998
MJD later renamed the dist to Algorithm::Diff
Algorithm-LCS-1.04 CHORNY 11-Aug-2003 unauthorized
Part of this source is used by AlgorithmDiff::XS
Language-Guess-0.01.tar.gz MCEGLOWS 02-Nov-2004
This isn't available on CPAN.
In both cases I worked around for my dists:
At least it's a little bit boring that authors "first come, do nothing".
It would be nice to discuss freeing the reservation of namespaces
after some time without usage. IMHO 3 years should be enpough.