The market is already incentivized; if the performance of your site is lousy, people won't like it. I think fiddling with SEO incentives is too big of a hammer to swing at what is basically a very narrow technical problem, overall JS parse volume.
The sad thing is people are so used to this modern web crap that I don't think they will stop using it. The Facebook "we crashed the app and users never stopped coming back" experiment comes to mind. Sure, technical users like anyone on HN will probably know what it could be like, but a lot of users likely have no idea how fast the web can be. A site that takes 2 seconds to load is "fast". 5+ seconds to load an article on mobile while the page is jumping all over the place is "normal".
