Feels like this would have been a good fit for zoned sharding in MongoDB -- hot shards that would age out to cold shards, never having to deal with the lack of

Feels like this would have been a good fit for zoned sharding in MongoDB -- hot shards that would age out to cold shards, never having to deal with the lack of strongly consistent secondary indexes or transactions, and not having to deal with a completely different database for the hot and cold environments.