[EME] Mitigating the impact of HTTPS on content providers

The main objection to requiring secure origins for some or all key systems
seems to be the impact this would have on content providers using MSE -
mixed content restrictions would require them to also serve the encrypted
media streams from a secure origin. While there is still some debate as to
the actual impact, I'd like to start a brainstorm and discussion of ideas
on how we might reduce the (immediate) impact on content providers while
enabling user agents to require secure origins (in a reasonable timeframe).

Here are some ideas to start the brainstorming. (I don't necessarily
support any of them at this point.)

   1. Define a flag day by which HTTPS must be supported/required.
      1. See http://lists.w3.org/Archives/Public/www-tag/2014Oct/0100.html.
      2. There might be some sort of timeline / phased-in transition.
         1. For example, ramping up the amount of HTTPS traffic.
      2. Temporarily allow Mixed Content XHRs to be provided to MSE when
   EME is in use.
      1. Non-secure XHR responses passed to MSE would temporarily be
      considered Optionally-blockable Content like normal video.src content.
      2. Given a choice, securing EME is probably more important than
      preventing use of mixed content with MSE. (The alternative seems
to be that
      none of the bytes are secure.)
      3. We would need to consider the security implications.
      4. This exception would be eventually be phased out as in #1.
      5. I'm not sure how practical this would be for implementions.
   3. Establish an informal flag day, such as an agreement among major
   browser vendors and/or content providers.
      1. The goal would be to prevent content providers from segmenting the
      platform by refusing to support user agents that choose to require HTTPS.
      (See the second to last paragraph in
      http://lists.w3.org/Archives/Public/www-tag/2014Oct/0096.html.)


David