I just had a discussion with a potential new client of mine who would like to have their site powered by XenForo. They are searching for a system that gives them this: http://online.wsj.com/article/SB10001424052748703886904576031510722493874.html
... so that normal users only see a portion of the text of their articles and members who have a paid subscription will see the entire text. This way they hope they can monetize the site better by stimulating people to pay for their membership.
Obviously XenForo is not a CMS/article based system (yet), but I guess publishing articles inside the forum (in the first posting of a thread, so that members can comment on it through the thread) will also do for this client for now. However, XenForo does offer forum-access connected to paid subscriptions, but no such thing on the posting/article-level.
I realize I am putting something into the Suggestions forum that not much people will need on their forums (I presume), so if it's more suited as an add-on (as I think it is), then please move this suggestion to a more appropiate forum.