I see rethinkdb as being focused more on the data model and language, and the cluster administration experience. The performance doesn't seem compelling yet, though they are admirably durable by default.

You're right, with a reliably performant engine you can get a lot more out of a single machine than a lot of people these days seem to think. That's part of our vision for TokuMX, to bring back a little bit of "scale up" potential to the NoSQL space.