Actually, this is a problem that is already solved by smart motorways in the UK (Europe too maybe?). They have a variable speed limit that dynamically changes according to traffic that stop brake waves happening.
If my experience with smart motorways is anything to go by they seem to increase brake waves because there are often times that speeds get reduced significantly for arbitrary reasons that not everyone chooses to follow. You then get larger closing speeds which causes people to slam on the brakes.
Additionally the removal of hard shoulders is just dangerous.
Do you not have them in the US?