svnadmin hotcopy --incremental

Somebody responsible for backing up a large FSFS repository asked me if
it were possible to do an incremental hotcopy. An incremental hotcopy
would update a previous hotcopy to the current HEAD and would only need
to copy the rev files newer than the previous hotcopy. This might
involve deleting rev files if the packing has changed.

Some strategy to deal with revprops would be needed: copy them all, read
them all and copy the ones that have changed, copy the ones with newer
timestamps, something else. The locks directory would need to be
deleted and copied completely.

Incremental hotcopy would start with a valid repository and end with a
valid reposiory, but interrupting it part way through might result in an
invalid repository.

I don't think we can easily do this for BDB, so this would be an
FSFS-only feature; since svnadmin already has BDB-only flags this should
not be too much of a problem.

Anyone see any problems with this approach? Does it sound like a good
idea?

-- 
Philip