It's tricky. Many (most?) researchers would rather have a closed discussion with other researchers with domain expertise than an open one where they have to deal with public comments.
I think this is certainly true. Research papers are typically written so that a person with training in the field can understand and replicate the work. Note that the general population is not the intended audience. Mediums like news articles and blog posts are a more effective way of explaining the background and significance of a certain piece of research to the masses.
Yes, but that's still hard if half of those other researchers are on Librarian, and half of them are on Hypothes.is.
I've always thought stack overflow could be the start of a model for an academic archive.