If your car’s dynamic performance became progressively worse as your fuel capacity dropped would you still find that acceptible? What if automakers actually had the vehicle become more efficient as it approached empty? Like your CTS-V is consuming all the fuel it needs for full power then it becomes a 530 hp engine getting 21 mpg average for the next 1/4 tank, drops to 400 hp getting 24 mpg average the next 1/4 of the tank, and finally going to empty as a 290 hp engine returning 28 mpg combined.
Personally, I would actually be ok with that for larger engines. Maybe the drive mode selections could control that aspect of the performance as well so that you end up with something like this for that CTS-V:
290 hp (28+ mpg average) for entire tank.
3/3 tank = 400 hp (24 mpg), 2/3 tank = 290 hp (28 mpg average).
3/3 = 530 hp (21 mpg), 2/3 = 400 hp (24 mpg), 1/3 = 290 hp (28 mpg).
3/3 = 640 hp (18 mpg), 2/3 = 530 hp (21 mpg), 1/3 = 400 hp (24 mpg).
Sport Plus Mode
3/3 = 640 hp (18 mpg), 1/3 = 530 hp (21 mpg).
4/4 = 640 hp (? mpg), 1/4 = 530 hp (21 mpg).
640 hp (? mpg) for entire tank.
And you switch mappings according to the drive mode and where the fuel gauge is. Also the car starts in the last mode you had it in. I’d be down for this since it would be like the larger the engine you buy then you get to drive every lower engine version of the car.