Considering the first line uses the word API I'd say I meant API
Said API could then be used to form the basis of cross site syndication or be used inhouse.
Well I wasn't disagreeing with the use of API, just syndication. To myself and I'm sure a lot of other people when I hear the word syndication I immediately think RSS. If by cross site you're including other servers you're talking about either using RSS, having a propietry export format sent across the net, or allowing direct DB access. All of which have big security concerns, the latter two probably more so.
Regardless of the syndication abilties you'll still need a simplified phpBB library which could be used in-site. I'd suggest breaking this request up into 2 mods. A phpBBlib mod which could be used in a fashion similar to phpbbfetchall and then a syndicator mod that would have a dependence on the phpBBlib.
Disclaimer: I'm surrounded by 7 empy cans of soda after staying up all night on a coding binge so I could be talking crazy