We purchased  simple mod in the marketplace that allowed members to view the contents of a forum in IP.Board 3.x , if they had 10 posts. It was a great incentive for participation.

Noticed in IPS4 you have a similar option but the forum is not visible until the nominated posts are made first. Is there a way that a member can see the forum but not the threads/posts until they reach the desired number of posts?

Should be doable by using the auto-promote feature for membergroups. So you need 2 membergroups where one can only see the forum and the other also the posts. After 10 posts, members are then moved into the first group.