I think it should be possible to change the database without too much effort. I also managed to replace the IndexedDB database with another one quite quickly without diving deeper into rdfstore-js (but can't find the link at the moment ).
What I still remember is that the important files to modify were:
If you want to see another database implementation, just look at the in-memory alternative (remove the "persistent_" from the links above). Happy Hacking ;)