But the beauty of the minimal Hacker News design is that users can create their own idioms on top of it, that, in effect, become part of the design - a domain specific design, or DSD, if you will. Crystallizing a common idiom into an explicit feature. with explicit design, would enforce a common interface upon all users, which despite its benefits would reduce the raw power and flexibility of the minimal design - a step along the road to Blubber News. ;-)
But seriously, it's a good idea; but why not do it within the current design? That way, you get voting on the summary too. Herring's point about RSS could be accomplished by including the top comment in it...
Polls originally started this way, and did crystallize, specifically, I think, because they went against the whole "comment karma is a real, useful measure of participation" idea. Likewise, just restating the article-but-shorter shouldn't be rewarded--pretend we're all in a sixth-grade English class: "Talk about the assigned reading; don't just say what happens."
But seriously, it's a good idea; but why not do it within the current design? That way, you get voting on the summary too. Herring's point about RSS could be accomplished by including the top comment in it...