It is doable.  It would also be a lot of fun.  For aesthetics, I'd like to limit moderations to containing only lowercase English letters.  And, as I mentioned before, it would make me very sad if "disingenuous" became a moderation on TNT, so maybe we could block that specific word.

In fact, funny story: When I implemented ajax moderation, I noticed a bug/security flaw/feature in the existing code.  Basically, it let people create their own moderation categories.  The drop-down provided only a few options, but if you edited your HTTP POST data, you could get around that easily.  (This is easier than it sounds; the Tamper Data Firefox extension makes it easy, for example).  So, for those who knew how to do it, you could put in any moderation you wanted.  This was a security problem, because it meant you could insert JavaScript code onto the page, and do crazy stuff like force people to click through 500 alerts or post their authentication cookie as a QuickLink.  So I fixed that.  But, no reason why I couldn't break it again.