revision library pruning

Hi, for revision libraries their major "problem" is the disk space that they
take. It may be useful to have automatic pruning functions; AXP has a
command to do that.  I would like to know what is the optimal way of
deleting selected revisions from.the library to keep the total size at some
threshold. For example, would tla tracking the number of references to each
revision (in the revision library) be useful?  I am thinking of, say, tla
keeps in a meta file the count of explicit references to a revision each day
(a "reference" here is a tla get on the revision or a tla diff on the
revision).  Then a script can select revisions not referenced too many times
in the past some days to delete, or some such.  The pruning itself probably
is not to be done in tla.  Would such an approach be useful?

Thanks for opinions on this.