We have no idea how many people have really been craving a hybrid Mustang from Ford, but the demand is obviously there because Fordauthority is now reporting that the Detroit giant is working hard on a Mustang with a hybrid powertrain, and it apparently goes by the project name S650E.
"Ford currently has an S650 Ford Mustang hybrid model in operation - known internally as S650E. It's unclear what sort of hybrid powertrain is present in this pony car - it could be a traditional hybrid or plug-in hybrid, however. It's also unclear if this project will ever see the light of day, given the fact that the Trump administration has worked to relax fuel economy and emissions regulations for vehicles as of late, in general. That said, S650E prototypes are running around and have entered the Technology Prove-Out stage, meaning there's mules being tested that likely feature some form of electrification."
Source: Fordauthority