There should be a way of making comments on other people's work. Right now all there is are the discussion pages and those are for contributor use only. I find this quite suboptimal.

I mean perhaps the idea is that you can make threads for that but so far it mostly seems that people use either one or the other. Probably because it feels stupid to post things twice. Even if one of the postings is just a repository upload (and of course you'd have to edit in two places).