I agree we definitely need users to able to create an invite without a pub, but I can see some problems with this proposal.

One thing: now for every user, there is also the temp user. to invite someone, you generate a private key, and send it to them. What if they started using it like a normal identity?

What happens with invites that don't get accepted? it would mean you appear to be following a bunch of people who don't really exist. Hmm, I guess there is the proposal to skip requesting feeds which havn't changed, but info about those feeds would have to be lurking around somewhere.