People (like me) often sign up initially because they have something to add on something right now (a space-flight article (my field) in my case), and rarely be

People (like me) often sign up initially because they have something to add on something right now (a space-flight article (my field) in my case), and rarely because they anticipate being moved enough to comment in 25 days. This proposed mechanism would especially preclude contributions from the people whose content is being featured, which you often see ('hey, author here, thanks for the interest...' etc) who sign up just to answer questions about their blog post or the bit of software they've authored that has got to the front page. To me this stuff has often has higher value than 80% of the comments from career commenters, just by virtue of the SNR to the discussion at hand. It would be a disservice to the community to preclude it, I think.