This suggestion is completely orthogonal to what ad companies want or need.

For example, you could include a unique identifying user ID with each request (for either profile) - this would actually make it easier and more explicit to track users, instead of trying to create an identifier out of 10 sources (cookies, fonts, localstorage, ...) in JS. You would probably also allow HTTP cookies in such a profile.

Incidentally, the push towards fast HTML subsets (Google AMP and Facebook Instant Articles) comes exactly from these big advertising / content companies! I think it is because it allows them more control over how ads are included in pages, and it allows them to keep users in their apps for longer.

No need to ask all ad companies. The biggest ad company in the world owns the most widely used browser. They can single-handedly prevent something like this from being standardized.