I wouldn't suggest limiting such a feature to higher level members. That would be like saying you have to be level 6 until you can enable the chatterbox nodelet, and can't view the Newest Nodes page until you are level 8. Of course, I just typed that assuming you only meant an additional scratchpad per user.
Perhaps a different system has been devised? By 'various permission models', are you saying something more like a wiki system, to which a user can say who is allowed to access it and what permission bits (read, write, etc) each user is permitted? If so, perhaps limiting by level would be okay, but couldn't we just increase the number of such wikis a user can have, based on their level (such as votes are done). That way, a level 2 or 3 monk can still use the feature, but will have a small quota. By level 7, a user could be given the power to have more such wikis :)
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