Users should be able to specify that their data should not be shared across multiple sites through the use of ubiquitous embedded subresources. This means that cookies should not be automatically sent in requests to embedded subresources on other sites unless the use has agreed. 1st party sites have the primary responsibility to offer this choice to users so they should have the ability, say by using a response header such as FP or CSP, to force 3rd party cookies to be siloed, as they are for example in Apple's ITP. The cookie siloing function, and its control mechanism, should be standardised.

Speaking from experience as a developer who writes and maintains single sign-on infrastructure, I'd highly recommend that any privacy controls take into account domain ownership as party of determining "party".  For example, looking at Google's TLS certificate, I see several dozen TLD+1 sites that are operated by Google such as goo.gl, g.co, youtube.com, etc.  Using "domain" or "TLD+1" for identifying a "party" makes it difficult for organizations that operate multiple "brands" from sewing together a cohesive, unobtrusive security experience.

Yes, this is important. Users also should be able to immediately see what companies are responsible for any embedded resources on a site. One possible way is for the third-party to signal this in a .well-known located resource, e.g. the DNT Status Resource at https://example.com/.well-known/dnt/ which is a JSON representation containing information such as the company's identity, privacy policy etc.

Thanks for filing the issue!

As per comment#0 by the reporter this seems to be a feature request hence marking it as Untriaged.

Moving to available - outside the scope of network bug triage.