I created something like this for PostgreSQL. It's a Node.js service that implements the MongoDB wire protocol and converts the query to use jsonb. It works pretty well, but it also got increasingly hard to make it compatible because MongoDB has a lot of quirks.
As a F/OSS freeloader, I would very much like you a link to this project... Feels like something I'd contribute to or do something crazy like try to start a business (2ndquadrant/edb style) on.
Thanks! I didn't realize I put the link. Here it is, http://github.com/thomas4019/pgmongo. I'd love to hear your thoughts on it and am happy to answer any questions.
