For me, I just wish MongoDB had scaling options closer to how Elatic/Cassandra and other horizontally scalable databases work, in that the data is sharded in a circle with redundancy metrics... as opposed to Mongo, which afaik is still limited to either sharding or replication (or layers of them). FWIW, I wish that RethinkDB had seen more attention and success and for that matter might be more included to use CockroachDB over Mongo, where I can get some of the scaling features while still being able to have some level of structured data.