One way to do it is for the big super speedways to have their banking lowered, creating a flatter track that requires some lifting or even braking in the corners, allowing the cars to separate from each other. That, of course, will never happen.
On the car side of things, I'm not sure penalites for coasting will help much. I think there would still be pack racing. I think they need to take away enough aero and mechanical grip on the cars, and up the power a bit, so that they have to lift for the turns. Even in the mid-1980s, they had to lift in the corners because of too much straightline speed and not enough tire or aero to handle cornering that fast.
Basically until you can find a way to make the drivers have to lift for the turns, you'll get pack racing, even without restrictor plates, ECU restrictions, etc (and obviously Cup cars haven't actually used plates for a few years). I was told It was the 2000 Truck race at Daytona that inspired the late 2000-2001 Cup aero package. Granted, the Truck series didn't run plates at Daytona or Talledega until after 2006 iirc, but still had pack racing leading up to that time - due to a ton of downforce and drag (ie as aerodynamic as a brick and running in 2000 9:1 compression engines).