I think the people who would be most interested would be the people who visit once, find that it would be hard, then go away.
I think a write up on how you did the conversion would make a great sticky topic. Even for people who don't come from phpbb, stuff like changing the WW password to MD5 is useful for lots of other people trying to integrate wwf into their site.
Most of the integration scenarios I've seen involve changing the existing site to wwf encryption mechanisms and having users re-register. I just love it when someone comes up with an approach to a problem at a 180 degree different angle than my mindset.