UP FOR DISCUSSION: - After driving BMW's M3 and M4, we ask: how will sports cars evolve? - Thoughts on the Cadillac ELR's failure to perform. - By 2025, survey says, 75 percent of North American pickups will be aluminum. SPECIAL GUEST: Mark Stielow, Program Engineer Manager, Chevrolet Camaro Z/28 - How and why his team developed a $70,000 Camaro All that and more with John McElroy, Autoline.tv; Gary Vasilash, Automotive Design and Production; Michelle Krebs, AutoTrader Group.