MySQL just announced a pre-release snapshot which comes with an integrated Memcached plugin accessing the InnoDB storage engine directly: NoSQL to InnoDB with Memcached
The ever-increasing performance demands of web-based services have generated significant interest in providing NoSQL access methods to MySQL. Today, MySQL is announcing the preview of the NoSQL to InnoDB via memcached. This offering provides users with the best of both worlds – maintain all of the advantages of rich SQL query language, while providing better performance for simple queries via direct access to shared data. In this preview release, memcached is implemented as a MySQL plugin daemon, accessing InnoDB directly via the native InnoDB API
I wouldn’t be surprised to see more of this kind of integration also from other DB vendors.