Greetings! I will not be on the call - it will be something like 2am for me. Simon will (hopefully) be there to cover the items 4, 5 and 6 for Apple. I've made comments on Github, and a brief summary below.
My summary is that this was intended to be intentionally vague - it was our alternative to "better" or "more-colors". Also, there are many variants of P3, so picking an exact one doesn't make much sense if you're just trying to get an idea of the display capabilities.
If you decide to go back to "p3", I can promise that Safari Technology Preview, macOS Sierra betas and iOS 10 betas will instantly support the updated syntax :)
I don't have strong feelings on this, other than please make sure that the developer never has to think whether or not she needs to put in a comma. As SimonP joked, we'll probably have to implement support for commas and no-commas anyway.
It wasn't clear to me if this was about defining a bunch of shorthands for popular color spaces (which I'm ok with), or requiring implementations to actually support a set of popular color spaces (which I think should wait).
If it is the latter, I'd be reluctant to include anything more than "Display P3" and "AdobeRGB" in a first version. If the developer wants something else, she can link to a profile (although we really won't want to download anything), or use a shorthand (and hope the implementation supports it). While this might seem restrictive, we're still giving them more than they have at the moment, and leaving the door open for future support.