I suspect there will be many new ways to fetch notes in the future (p2p overlay networks), etc. nip01 just defining the packet is good.
I picture nips branching out as a tree. Maybe there is a root node that defines social networking nips, that specifies the outbox model as the way to fetch notes for that class of applications.
So in that sense I agree with nostr:npub1acg6thl5psv62405rljzkj8spesceyfz2c32udakc2ak0dmvfeyse9p35c if this is what he means, but there will be other root nodes for other application domains with different ways of routing notes.