A wire-protocol for debugging/live reload/etc. would be awesome, but especially if it's cross-browser! As an IDE developer, I shouldn't have to do one thing for Chrome, and one thing for FF, just to support the same operations (like set debug point, step in, step out, etc.).
Obviously, yes, they'll be a different set of features at first, but for the overlapping ones, the wire protocol should be the same.
Just look at how painful things were for Selenium/Webdriver; which I now see is moving into the W3C. Hopefully that makes their lives (and our lives as developers) easier if the browsers share a protocol.