Ok- we have a few opinions favoring simplicity.
Here's my next re-imagination of what could be.

The "page" currently can probe for some details of what's looking at it.
YES, that's an oversimplified explanation but for this concept it works.
So- as is already done by some sites- the "version" of what you see
is selected for your device or connection or both. But can we go a bit farther?
As in an agreed upon default backchannel in the browser to tell sites

"Show me <Blank> and do not ask me <blank> that GETS HONORED.

The reward is:Sites honoring such a scheme will get customers
pre-selected for parts of the site's content and not annoy customers
with unwanted non revenue content
 Which to me is that flood of "Plug-in" demands and the constant
 begging us to update our <Blank> "To fully enjoy this site"
Or the more grim- it simply won't play at all with non-genuine MS.
Believe and puke- there are plans afoot to tie WGA to browser access!
.
And sadly we still have to code OUR sites to play nice with windows.
Now the inversion of course is sites hostile to non-explorer browsers.

I put it like this- while one has a "right" to make sites allow or forbid
certain browsers in personal work- "Public" sites  such as government
or educational do NOT have a "right" to block handicapped or nonMS users.