Is ZopeUndo.Prefix still used?

I'm trying to remove instance pickling from the ZEO message protocol. Currently, the only instances ZEO clients are allowed to send (in the messages themselves, not in database pickles) are ZopeUndo.Prefix.Prefix instances. I'd like to remove this special case.

If the use case for this still exists, I'd like to explore
alternatives on the ZODB mailing list.