Johm builds allows to use data types on top of Redis. I implemented the ability to query multiple fields at https://github.com/gersh/johm. I've been discussing ways to implement more complex queries on Johm mailing list.

Currently, I believe Redis has enough functionality do a lot. I think it should be possible to build more query-like features on top of Redis, and preserve more flexibility in terms of how the querying works. Then, you could decide how far you want to go with SQL-like functionality.