I think that would be fantastic. I have envisioned that kind of thing often. Something like "autodidact.stackexchange.com" (which doesn't exist), for example. The best explanations could be voted up. For bigger topics, it would not be explanations you're voting on, but rather "learning roadmaps" -- a recommended set of materials in a recommended order that is designed to help one grok the topic.

For academic papers, perhaps people could vote on two dimensions: (1) papers you'd like to see explanations for, and (2) particular explanations that were effective for you.

And yes, I would read the hell out of it, and yes, if there were areas I could contribute, I would do so.