Interpeer aims at peer-to-peer interactions also at the software level. AP aims at person-to-person interactions, arbitrated by servers on which the respective persons "live".
It seems eminently possible to imagine an AP server that contains a bridge to the future interpeer stack, or that is just a bridge. This should enable fully distributed social apps, that can still use the federation capabilities of ActivityPub.
That future is very exciting! But we have some ways to go for that yet.