Nay, Nay and Thrice Nay
This is a malignant at sooo many levels.
google.com and google.co.uk are owned by the same corporation (*). There will be many, many cases where foo.com, foo.org, foo.co.uk and foo.eu below to different organisations. How will a user be able to give informed consent for blanket cookies to any of the foo?
That youtube belongs to google is (sort of) widespread knowledge. How does the average user know who "newly_aquired_startup.com" belongs to - the original founders, or the megacorp that bought them yesterday? And next week, when the megacorp sells them on? Which entity owns the blanket cookie then?
If I need to enable cookies in order to access a .gov.uk website, does this give the government carte blanche for a blanket cookie? Or does Crapita (provider of the service behind the .gov.uk) get the blanket cookie? Or do both get a golden ticket?
(*) They'll point out that they are discrete entities when they need - tax reasons, for instance.