A benefit to JSON is that people know immediately what it is. It certainly does have its deficiencies (binary data being one that outweighs dates in terms of

A benefit to JSON is that people know immediately what it is. It certainly does have its deficiencies (binary data being one that outweighs dates in terms of immediate importance). Being limited to strict JSON is not a permanent decision (I'm saying this as a member of the RethinkDB engineering team), it's a conservative one in terms of API design, and in terms of limiting scope for the first release.