If they don't, that's hardly the end of the world. Topics evolve in real world conversation all the time, that's how people think and make connections. The ques

If they don't, that's hardly the end of the world. Topics evolve in real world conversation all the time, that's how people think and make connections. The question's really how you organise things - how you filter attention, and what tools there are for that to allow people interested in certain aspects of the discussion to see the bits they're likely to be interested in. Not every video needs a full blown forum underneath it, but I honestly doubt that one would occur even if you made the threads groupable at arbitrary levels - there just wouldn't be the static central point of contact with multiple people checking back that a forum seems to need, (i.e. I can't imagine people would keep on and on reloading the video,) and some sort of decent threading seems strongly indicated. If you lack such tools, it seems to me that the only things people are liable to post if you take the length restriction off is the full text of books to try and crash the browser, ASCII art of male genitalia, and links to some of the more ewww corners of the internet. In the time it takes someone to post something well thought out someone can post twenty ASCII penises after all. The low-effort to high-lols expressions seem likely to dominate over the high-effort high-meaning expressions. Sort of like how Reddit decayed, but with a somewhat darker tone since the existing community in the comments is less well developed than they started off with, there'd be even fewer tools, less effective moderation and you won't be able to hide niche communities behind unknown lookup names as well.