When was the last time you visited? Ignoring our other channels (many of which, including News and Lit (née Poetry), have been in place for a long time), we've been working very hard to decrease the "geekspeak" and unfunny humor annotations. Guidelines have been in place against these types of annotations since I've joined over 12 months ago, and we're still trying to work through the 3 year backlog of bad annotations, while keeping up with the new stuff. Try looking at some of our more popular pages, or some of the stuff on other channels, such as news.genius.com. There's a lot of value possible in annotating, analyzing and contextualizing primary sources!
One thing that would be a very natural extension and really useful, would be annotations to scientific papers and books. I can't count the times I had to laborously fill in the arguments deemed trivial or obvious by the author, but were not terribly obvious at all. arxiv.org hosts a lot of them in source form, so modulo licensing issues and a good latex to html compiler, one could easily make them available for annotation. Other than that there are probably lots of interesting works that are in the public domain.
Obviously using "genius" and "iq-points" are just marketing and the number of rap fans are probably greater than the number of academics. So I don't know, if that is a viable thing to add.
