The Merriam-Webster dictionary defines muscle cars as "any of a group of American-made 2-door sports cars with powerful engines designed for high-performance driving."[2] A large V8 engine is fitted in a 2-door, rear wheel drive, family-style compact, mid-size or full-size car designed for four or more passengers. Sold at an affordable price, muscle cars are intended for street use and occasional drag racing.
By that definition alone, the Muscle car died in the 70's. It's not even the fact that most modern performance cars are 4 doors or fwd or awd that doesn't classify them as a muscle car. It's the affordable price part that killed off the actual muscle car. Now a day's the performance car is the most expensive, not the stripper model with a powerful engine.