The Website Obesity Crisis
For all the effort that browsers go to in order to make sites "scary" when there are bad certificates, etc. I would love to see a big, red, scary page that says "you are loading a web site that is consuming an unreasonable number of resources, are you sure you want to continue?".  Make that the default, make the warning limit 400 K, and watch web sites (complain first, and then) change.