Any idea why not?

My first guess would be that a big part of the target audience is lurkers, who shouldn't be expected to post all that much.

From what I've seen about the glacial pace of edits to site mechanics, this is almost certainly not going to happen. Unless you know of an easy way to do it?

Changing the sidebar is the main thing that I have seen happen; I do think it would be much more likely to happen if a volunteer writes the required code.