If you're interested in building a distributed DB on top of LMDB, I took care of part of the problem (replication/consistency) in my flotilla library at

https://github.com/jbooth/flotilla

Basically I'm just layering the raft consistency algorithm on top of LMDB. Both systems single-thread write transactions for consistency, so there's some mechanical sympathy. Doesn't mandate any specific data model or even a client-server network transport, it's basically a replicated embedded DB. Anyone could build replicated redis on top of it or a Cassandra clone if they want to get into managing shards/rings.

Sample app (still WIP) at https://github.com/jbooth/merchdb