I am currently using VBulletin.
I currently can hide all posts in a thread, except the 1st post (as a means to increase registrations)
In other words, anyone can read the 1st post in a thread, but subsequent posts are each shown to guests as "This post hidden to guests - sign up and become a member to read (free to register)". Members can of course see the content in the post(s).
So if there are 4 posts in a thread, anyone (i.e. guest & members) can read the 1st post (the starting post) but guests see "Post hidden to guests etc." three times, for each subsequent post. Guests can however still still see the person making the post, just not the content.
I hope I have explained this clearly, it really made a difference to our registrations, as people get drawn into an interesting thread title / 1st posts, and then want to read subsequent responses / answers, so they register.
Is this in the core with XF 1.5?