I attempted to do some work along these lines in the fix-rdump-editor branch, but was unsuccessful.
That experience in attempting to rewrite svnrdump to use proper file and directory batons is that it
probably won't happen with Ev1. The dump file format is much less amenable to streamy generation from
the piecemeal callback paradigm that Ev1 provides, and the right (and probably easiest) thing to do at this
point is just implement svnrdump using Ev2.
Hopefully replay grows support for Ev2 soon-ish, but I am concerned that this will become a blocking issue
for 1.8, as additional work will need to happen for the RA layers to support Ev2.