Arguments are the following:
1. Data corruption is possible due to implementation bugs. We have had
a lot of bugs in revprop packing feature and the proportional amount
of bugs is possible in this feature. We are unable to identify these
bugs before the release due to obvious limitations of alpha and beta
testing.
2. Data corruption is possible even if user doesn't actually
upgrade to the new format (because of the broad changes in the FSFS
code).
3. We haven't implemented the improved testing discussed in [1].
4. Despite the possible bugs, maintenance burden will be increased
significantly. We are introducing additional FSFS format that
dramatically increase the code complexity, because we still have
to read and write *all* FSFS formats multiplexing to different upgrade
path combinations.
5. FSFS7 introduces big code duplication because a lot of features are
actually copy-pasted from the experimental FSX format.
[1]
http://mail-archives.apache.org/mod_mbox/subversion-dev/201311.mbox/%3CCABw-3YdV1YX0yU3cuWD8syPGpQxkLBUe=6h_bMkuBfA+vQf9XA@mail.gmail.com%3E
Bug
Major