I'm using V3.1.4, It was in a ticket where a IPB staff told me I could request this. He told me that this feature was not in any boards.
The only permissions I know of in my version are forum permissions and group permissions. There is clearly not a feature like this in any settings. I don't know if you fully read the first post because I haven't even seen this in the newest version.
The main purpose of this topic was to request a system that replaces links with: "You must be a member to view this link, please sign in or register" Something like that.
I've seen on many boards(mainly vBulletin) of a unique system. If your a guest viewing a topic you will see: " You must be a member to view this ..." when viewing downloads or links. It's very useful as people would then sign up to view the content in the post. It attracts more people to your board which is the main thing for many boards.
I'd like to see this in a future version of IPB. It's extremely useful and beneficial.
If it's never considered to add it, well I hope at least a hook or modification is made to do this.
I have noticed many past spammers that I have dealt with myself are listed in this database. I am getting hit with spammers daily so I have now installed this mod. I hope this takes care of my problem.