I am a little familiar with the Fabula Ultima system. It does seem scaled back enough that it would make for an interesting system to use for PbP RPs. I really like how the Fabula point system allows everyone to tell part of the story, how you mix and match classes to make a unique character, and how tests are performed. It's not a perfect system, but I doubt there are many low complexity systems like it that manage to do so much with so little.

It looks like you have a full party, but I may join if someone loses interest and the RP looks like something worth joining.