I apologize for being slightly off-topic. I think an open-source PDF -> HTML 5 renderer would be extremely useful and potentially disruptive. I suspect it would produce lots of experimentation into the right way to read, annotate, and manage documents.

This wheel has been reinvented now at a few different companies. Is anyone aware of any projects actively building an open source canvas renderer?

While it would be great if crocodoc open-sourced their renderer, I'm sure their business model rests (partially) on the difficulty for others to enter this space.