There's async libraries here: https://github.com/facebook/tornado/wiki/Links - You can get just about any db except MySQL. There's ones for Couch, Mongo, HBase, a bunch of other No-SQLs and Psycopg (PostGres).
Also, Tornado is now introducing some kind of interface to Twisted's event loop, which does have everything ported.
Bret just doesn't seem to want async My-SQL in the main code base.
Disclaimer: I wrote an async DB module for Twisted/PostgreSQL and it did not turn out to be all that complex.