I voted for 1970, but realize that is probably not very realistic. To make the car affordable for consumers, the Challenger replacement will need to share a platform with other cars, either the new Charger platform or the Avenger-replacement platform shared with Fiat. One of the reasons the modern Challenger is so large was to make the retro styling work with the much higher cowl of the Charger platform. It is a safe bet the Challenger replacement will be smaller and lighter, but you aren't going to see a 3,500 pound RWD V8 hemi. For perspective, the much smaller V6 powered G37 weighs 3,633 pounds. A supercharger and related suspension & driveline upgrades could easily add 100+ pounds to a naturally aspirated version. Given looming CAFE mileage increases, Dodge is going to want the car as light as they can possibly get it. My guess is this will require a more modern look with some retro cues, since trying to replicate the proportions of the original cars tends to make the car bigger and heavier.