Rough draft of EME Concerns document.

As discussed in various forums, this is a version of the opinion document that tries to catalog our concerns for EME as a web-facing API, without suggesting solutions or focusing on specific technical choices or problems with the current mechanism. Feedback definitely welcome.

I like that a lot. Indeed, I wasn't trying to say "EME must work with any key system," but I can see how what I said might be interpreted that way. Maybe insert your sentence after the first one of this paragraph?