> it's not like you can ask questions about a random paper you are currently reading
In the early days of the web, I remember a service that allowed you to comment on any page on the web. I think it used frames. It embedded the page you were looking at into a frame and allowed anyone to comment in the margins -- it looked a lot like Fermat's Library. Unfortunately I can't remember what the service or start-up was called.
I thought it was a great idea and very democratizing. You could comment on a newspaper article even if they didn't allow commenting. You could comment on Coca-Cola's page or anywhere on the web. What killed it wasn't spam, advertising, trolling, or inane YouTube-style comments. Certainly those would have been problems to deal with if the service got really popular.
What killed it was copyright. Some company sued them out of existence because they were ostensibly violating copyright by embedding someone else's page.
So, as I understand it, it's not like you can ask questions about a random paper you are currently reading, and ask the community for help.