I've looked into RethinkDB and I really like it but… you have to migrate your data between each 1.x -> 1.y release which might be trivial early on but impossible at a larger scale :-/
Wow! That's a huge leap forward. I can look seriously at RethinkDB again for a new project. Is there a public roadmap where I could have seen that coming?
http://rethinkdb.com/stability/