Hi,
The first wfrog versions used Firebird. Latter we added support for CSV files to be able to simiplify the installation process. mysql support was also added because its popularity and a more wider availability than Firebird. wfrog does a very simple use of databases and therefore it is easy to add new drivers.
SQLite supports multiple processes accessing a database but only one writter. This is fine for wfrog. It also has a compatible python driver. There should be no problem adding support for SQLite. You can find the database driver factory in wfcommon/database.py and the specific storage engines in wfcommon/storage/firebird.py and wfcommon/storage/mysql.py. If you are interested in pursuing this line I could also help should you encounter any problems on the way.