We're talking about deprecating the BDB-based backends Real Soon Now. I suppose this should be done in OpenLDAP 2.5, but we've pulled a lot into 2.4 that we had originally slated for 2.5, which keeps pushing any actual 2.5 work further into the future as we keep extending 2.4.

At any rate, LMDB is settling down pretty well now. The only reason left to use BDB today is if you're working with a >2GB DB on a 32-bit machine, and frankly if you're doing that, instead of just upgrading to a 64-bit machine, you've got other problems.