A P2 surface does not need to become a new content system. The useful part of the idea is the rhythm: open the site, see what is new, write a small note, and follow the thread when a reply deserves more time.
Osbirds keeps that rhythm inside ordinary WordPress. The feed is made from Posts, the reply tree is made from Comments, and the archive remains searchable after the first page has moved on.
That boundary is not a limitation. It is what makes the theme replaceable. A site can change its visual surface without losing the writing that gave the surface a reason to exist.