I hope it's smaller, lighter and modern looking. Keep the drive trains as they are in a smaller, lighter car with a tough IRS and it will be a real performer.
Consider this....
The base 2015 Mustang will have an EcoBoost 2.0 making about 250 hp. It will get excellent fuel economy and, since the car will be smaller/lighter, have good performance. The "entry level" GT will get an EcoBoost V6. It will deliver about the same power and performance while delivering better fuel economy. The GT premium will retain the 5.0 with direct injection.
Why do I dare think and speak such heresy? Because...
1.) Ford's most recent launches have all moved toward smaller engines with EcoBoost.
2.) Ford has stated that EcoBoost will be across all platforms.
3.) Fuel economy is the super hot button issue in the automotive world right now.
4.) Ford has, in the past, done what was not popular at the time because they felt it was the correct thing to do business wise.
5.) Leveraging the 5.0 as a premium model power plant will make them more money.
6.) CAFE, CAFE, CAFE. Gov't mandated Corporate Average Fuel Economy