failing to load make essential web applications useless? That sounds like hotlinking of images which I've always understood to be a dickhead move on the part of web designers.
Some web sites tolerate or even encourage hotlinking for specific images, especially images that the web designer reserves the right to update (such as the "right now on eBay" logo used by eBay API clients). Remember the old image-based hit counters from the GeoCities era?
As for the registering of the CDN, I think you misunderstood me. The site itself would register a CDN as part of the domain through instructions in the XHTML.
That sort of "registering" a particular CDN for a particular URL would be little different from just hotlinking.
I believe this would simplify work flow and allow you to swap out a CDN without touching a single line of code in the rest of the site.
I'm starting to understand what you mean if these CDN registration rules look like, say, HTTPS Everywhere rewrite rules.
Even better, you could register known external objects that are community approved.
Approved by what community?
Meaning, your XHTML does not have to reference the exact Google Analytics script, but to a common reference point that allows Google to normalize that code to whatever they want.
That can already be done with the existing URI framework by placing the reference point as a path within a hostname under google.com.
Privacy laws could be amended to state that bypassing the user preferences in the browser is illegal. Wasn't Google guilty of that anyways with something?
Netflix could tell it was blocked and pop-up a dialog box informing that certain features will now be missing AND list them.
Any other site could likewise social engineer users into turning on tracking by arbitrarily disabling features until the user enables the tracking.
If the user base sends out a message loud and clear that says, "Don't Track Me", I don't see why they get to continue violating privacy.
Web sites could implement DNT but use both carrot and stick to social engineer the user into turning off DNT. The carrot: "We know you're tired of seeing advertisements that aren't relevant to your interests. For example, single men probably don't want to be subjected to ads for feminine hygiene products. To make sure you see the most relevant offers, please disable Do Not Track in your web browser." The stick would be to arbitrarily disable features: "Some features of $sitename require a subscription or an invitation code. To get your invitation code sooner, please disable Do Not Track in your web browser."