You'd need databases that were open to splitting out and layering like that, and I don't think any major SQL databases are. (I mean, most SQL databases are still written in C-family languages; splitting out the PostgreSQL parser into its own library took 20 years and still hasn't really been done properly, they do some weird sync thing from the mainline postgresql codebase rather than being the actual trunk for parser development and having postgresql proper use it as a dependency). Maybe you could do something with H2?