Arnold,
Due to the work by Doug Blank on database backend separation, Sqlite databases can be used in right now in the development version of Gramps. This will be the future Gramps 5.0 when released next year.
See:
http://www.reddit.com/r/gramps/comments/38ases/gramps_50/
Database Design for Genealogy Data - Blog comment by sam888 - 25 Jul 2015