Technologies like this are clever and all that, and would be fine if they were used absolutely and completely sensibly and responsibly (I know, I'm idealising, but just let me have a moment!)
An ISP could use it to display a ONCE OFF message each browsing session, say, progressively more frequently as a user reaches their bandwidth limit for a month... or even if there's an update on a high-priority customer support ticket... one off messages I mean.
But ISPs would never do that, and from getting released to the first ISP using it for selling ad space will be no time at all.
Has to say where does copyright come in all of this? Is a company's webpage said to be defaced if it's plastered with ads without the permission of the website copyright holder? Does it infringe copyright laws or not? I dunno. I am not a lawyer!