LMDB should flush to disk
When LMDB support adds new zone, no change occurs immediately in its view_name.nzd file. Unlike plain file view_name.nzf, changes are not stored immediately to permanent storage. I admit it would have much better performance, but I think save to disk should be possible without restarting named.
named should allow automatic flushing to disk on some events. Be it periodic timer maintenance after some time or manual rndc call, for example during sync without zone name or for zone added via rndc addzone,
mdb_env_sync should be called sometime. It is never used in current implementation, on any event. I think data safety is important too, not only performance.
It is especially problematic on distributions, because LMDB support cannot be disabled once its support is built-in. NZF files were much slower, but were more safe.