A fairly pointless feature if you ask me. A crowd wall would be more useful. Set a threshold on the content, and then unlock it for all publicly once the threshold is met.
in a perfect world its a post that can only exist on specific relays, but its a bit like delete/undelete so depends on relays to honor the special flag on the post.
Practical examples using this are the 2 relays nostr:npub180cvv07tjdrrgpa0j7j7tmnyl2yr6yr7l8j4s3evf6u64th6gkwsyjh6w6 just released:
Discussion
A crowd well is generally an interesting feature but I think it works well for a specific content, but it's not applicable for a continuous steam, like a feed.