"See only first post" - Permission for implementing public previews for non-members

Reason for request
Show public previews in public discourse topics leveraging the SEO benefits and still enticing both anonymous / logged in users to become paid members

Ghost has this feature where non-members will be shown a public content preview at the top and a subscription prompt at the bottom - Public previews

Existing Discourse Option
In a limited way, it is implemented in discourse via gated topic theme ( this will work only for anonymous users but not based on specific groups ) - Gated Topics in Category

Proposed Solution
What would be ideal is a permission system like see only first post

This way, we can assign permissions like the following

Everyone - see only first post
Members - see all posts

Now we can write a public preview content in first post and rest of the content in subsequent posts

Kindly indicate if there is an existing way to achieve it in discourse.