[sdellysse]

How about a "silent shadow" system? When an account reaches a slope on the negativekarma-time graph, just make it so that a very small, random group of users are the only ones who actually see what they posted. To everyone else, it would be as if they hadn't posted at all. All the while, if what they do post gets a large percentage of upvotes compared to the amount that see the post, shorten the "shadow silent" accordingly.

It will not be made known to the user that their posts cannot be seen. They will have no reason to use alts, and we will have no reason to IP tracking, which could affect non-troll users.