The amount of people that will understand what that means is not very substantial. Usually asking for more permissions confuses users as well, people get permission fatigue.

i don't think that would work.

request for location doesn't require the page to explicitly indicate a desire, the request is triggered if the page attempts to use the location services of the JS API. sites that want to run unthrottled can't be identified simply by the usage of a certain API, so the developer would need to add something explicitly to their markup to indicate the desire.

i want control over the feature regardless of whether or not the site's developer deems it appropriate.

I really don't want EVERY website I visit to do this (at least in a pop up).

That's less "backward compatible" than the suggestion to pop up a dialog on switching to the page, because the page needs to know to ask for the permission.

I'm not sure if that's a good thing or a bad thing. After all, backward compatibility is how we got the semantics of an alert() dialog stopping all JS execution.

These days, due to my annoyance with pages reloading themselves when switching to a tab, I'm really not interested in packing more functionality into the whole tab switching mechanism. Like the back button, it should not be visible to web developers.

Every website would start showing such popup. Now (if you have enabled Javascript) many sites show popup to allow notifications the moment you open them. That is annoying when you search for something in Google and have to click "No" for every new page opened.