Ben (the guy in the video) is working on SQL support!
https://www.youtube.com/watch?v=EJzulpXZn6g
Here's a follow-up talk he did:
https://www.youtube.com/watch?v=zSI68J9wNJ0
Also, there's prototype-grade support for Redis:
https://github.com/meteor/redis-livedata
And that's just the beginning. There are lots more databases that will follow: https://www.meteor.com/full-stack-db-drivers