Spiky:

Yes, there is no reason why you can't use the Zone 2 buss as a tape out for a different input than the main room if that's what you need.

The problem with "coping with a changing HDMI spec" is just that" the spec is changing. It is now at 1.1, and about to go to 1.2. Beyond that, there is likely to be a 1.3, and there is no guarantee that a 1.2 design will be software upgradeable; it may require a hardware change. Keeping with DVI is a safer bet for now.