Nostr can easily develop the same problems email has

Email used to be an open protocol where anyone could run a relay and anyone could host a server

Emails were forwarded around the network on a voluntary, optimistic basis, and it worked well

But email didn't have a good way to prevent spam except by blacklisting ip addresses, which turned into a cat and mouse game, and eventually instead of massive blacklists, companies realized email worked fine on a whitelist basis where they only send or receive emails from certain big providers

The exact same fate hangs over nostr unless better incentives are built around it, e.g. paid relays, and that will probably only work if users are okay with a "pay to post" model

In four years nostr will either be dead or a paid service