Terrific application and amazingly full of features considering how new it is. As an interim measure until you manage to include a feature to import tile files into the database, I'm writing a Perl script to do the job.
I can see from the structure of the SQLite databases that it's designed to have multiple store.sqlite.n files (presumably because otherwise the store could get ridiculously large: it looks like my 200 000 tile files would make for a file of about 2G). What logic do you use to decide when to create a new one? Is it when the last one gets to a certain size threshold?
Once I've incorporated that into my script I'll post it here for anybody who might find it useful.
Looks like it's a slow process if you've got a lot of tiles, though; my current test job has been running for about 90 minutes and has only imported 13 000 tiles.