The main reason I didn't use AP is that it's designed for federated servers and uses a mailboxes network which doesn't fit with Dat & P2P. We may find a way to interop, but it'll require some kind of bridge service, and I didn't really see the point of adopting their schemas if it didn't buy us interop automatically.
Coming up with yet another format in that space makes that kind of bridge service more annoying to create though, especially if the format grows more complicated. E.g. just trying to bridge a few of the existing choices like Atom, AS2 and microformats has an annoying amount of edge cases.
Edit: also, thanks!