Sounds like an interesting project Bob!
I looked into YAF before building the mojoPortal forums but it did look like it would be challenging to port to other databases so I decided to start from scratch.
YAF is definitely more feature rich than our current forums.
To me the challenges of integrating it into mojoPortal are:
- database porting as you mentioned
- design integration into mojoPortal skinning
- membership/authentication integration
- multi instance and mutli site integration (ie mojoPortal can have any number of instances of any feature)
I'll be interested to hear more as you progess, its nice to have more options available to mojoPortal users.