What a weird coincidence that this would really help let's say a company that used google.com as well as google.co.uk and doubleclick.com as their "first party" set. Good that W3C stopped it.
W3C doesn't really have any real power over what happens in the internet today. It's browser vendors associated with WHATWG that draw the straws now.
We're quickly approaching the third "E" in "embrace, extend, extinguish."