Hopefully we can put this part of the thread to rest.
I will try to summarize my conclusions based on the vociferous
feedback I have heard and then throw out some compromise roadmap
suggestions that may be workable and helpful:

- While a hybrid database/filesystem approach would certainly bring a
 number of advantages in some areas, it also would require a lot of
 work and would introduce a host of potential
 stability/robustness/speed issues. Most such issues are probably
 solvable but few would be willing to risk switching to a new
 approach until it was proved stable and there is likely to be little
 if any interest in investing in such an effort in advance of such
 proof. Other people are not interested in a new approach simply
 because the current approach satisfies all or most of their needs

 Recommendation: Keep as-is

- While there are block-level approaches to copying/moving the
 BackupPC tree, a continuing stream of users still would be
 interested in a file-level approach. Additionally, the ability to do
 "incremental" backups would be welcome. Holger, myself, and perhaps
 others have at times in the past suggested various O(n log n)
 algorithms for copying the tree & hard links using the known
 structure of the pool and pc trees. Myself and others have also
 suggested potential ways of doing incrementals either by tracking
 changes or by identifying changes on the fly (with the key 'gotcha'
 changes being the chain renumbering). None of these approaches
 appears to be particularly difficult though it does require a
 commitment of time