And furthermore this most base style of commentary is emerging: Thumbs up or thumbs down. Some sort of colosseum we're all entering! It's odd; I feel in the end it must be a phase. But for the moment it's unquestionably better than what we had before: Comments used to be almost universally sorted by date, which leads either to a scrolling empty newness or to the even bizarrer world of "first post!" Community editing is surely imperfect, but compared to that unfiltered firehose it seems a dawning light of rationality.
So those two parts together form a somewhat working system: Everything allows comments, and colosseum filtering makes those comments relevant and rational. Until something better comes along, I expect that model to gradually permeate everything.