PoW endorsements can be computed by specialized miners, because who computes them isn't important.

I am not talking about PoW on every note. PoW endorsements are like PoW keys, but better.

However, that's not necessarily useful for new users. But then the question is, how can someone enter nostr?

Maybe the answer is that they need a invite of some sort to surpass the "reputation threshold".

E.g. the user gets invited by someone and that someone automatically follows them.

Or, the user gets invited into a NIP29 (?) community, and so proof of membership in a reputable community can be used.