I believe that cost is a barrier to making changes. I agree with that and momentum/not wanting to make changes unless necessary are barriers to the Mustang even becoming a couple hundred pounds lighter.Taking today's marketplace into account I do believe that i am a realist. I worked for a manufacturer for 24 years so I know a little about the process. There are huge costs involved in making something a little this and a little that. The S550 was a major change for Ford and the $50K price that we were all complaining about in 2015 now seems like no big deal. Will Ford plan another major change for the S650. Maybe but I doubt it will be in the direction we would all like to see. If you were Ford, what would you make? A 3600 lb. crossover SUV or a 3000 lb. 2+2 coupe. Of course we want the latter but the beancounters will want the SUV. Now that's reality.
I doubt a well-designed modern V8 car can get to 3,000 lbs and be affordable, but 3500 or lower would be a win in my opinion.