Definitely my biggest current beef with Meteor. It seems technically possible and I understand why they would go with Mongo first, so hopefully its just a matter of time.
This looks good with the videos. I'm contemplating building an app that requires SQL. I've built a few apps with meteor but mongo's lock keeps crashing my website down.
The current third party packages with SQL support are very experimental and don't support nearly as much as the native mongo driver.
I assume when Meteor does this or if Arunoda does it would be pretty awesome. Especially with PostgreSQL since it supports native live queries.
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