Nothing about this is different than what exists today. Anybody can, and many sites already do, host their own copy of ga.js or google fonts or anything else s

Nothing about this is different than what exists today. Anybody can, and many sites already do, host their own copy of ga.js or google fonts or anything else so that all the resources come from their own domain. You can still block the effects by preventing access to the domain where the ad info is coming from.