svndumpfilter not supporting delta dumps?

Can someone please remind me why svndumpfilter refuses to work with
version 3 (i.e. delta) dumps?

What needs to happen to enable this functionality? (This makes
filters on large repository dumps a giant PITA as it has to work off
non-delta'd dumps.)

Thanks. -- justin

---
% svnadmin dump --deltas test | svndumpfilter exclude test
Excluding prefixes:
   '/test'
SVN-fs-dump-format-version: 2
svndumpfilter: Unsupported dumpfile version: 3
* Dumped revision 0.
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