The first thing you mentioned, annotations, or maybe even inline Q&A/discussions, was my dream in grad school (math). I imagined something like a separate MathO

The first thing you mentioned, annotations, or maybe even inline Q&A/discussions, was my dream in grad school (math). I imagined something like a separate MathOverflow for each paper. The basic problem is that I was constantly finding myself struggling with a tricky part of some paper from the 70's ("Why is this sentence true??"), and I knew many students before me had struggled with the same section, but there was no way for one really great expositor to clarify it, get upvoted, and be done.