A "Topic Of The Week" page, that gets deleted every seven days.  Someone chooses the topic, and then it is a free-for-all until the time limit is up.  If at any time something valid to Wiki is encountered, that can be spun-off into another page(s).  Deletion could be automatic (software driven) or manual (WikiGnome driven).

This would be a very good idea for serious Wikis like this one.  Would create a place to spout-off without polluting Wiki with a bunch of OffTopic pages (although I am one of those that thinks that anything that is of interest to the users is OnTopic).

This could start as TopicOfTheDay that spins off into TopicOfTheWeek, no topic OffTopic.

Spurs conversation, readership, usership, participation, etc.

In past years, just as with controversial/colorful users, multi-topic/controversial-topic pages (and HolyWar''''''s) bring about high-volume users/readers/participants.  The more outrageous, the better...