Since all cars are now "spec. bodies" then why not use this fact to do away with restrictor plates.
It would be easy to mandate a body that punches a huge hole through the air which would make restrictor plates unnecessary because the aero limits speeds.
At the same time, they could design the body such that "two car only" drafting gives no advantage over multi-car trains or...........make bump drafting a supremely unstable venture.
Before bump drafting, there was "the slingshot" and it was exciting because the draft at that time only worked on the straights because the second car in the draft experienced either lift or stability issues.
They can use the spec. body to do away with restrictor plates and bump drafting with a single body change and the non-restrictor plate engines would offer much more exciting racing.