Yeah, it's already thin enough. The 4S was thin enough. I would rather have a phone as thick as the 4S with a battery that outshines all competitors than a phone that is thinner. Thinner just means more fragile. Phones shouldn't be fragile. We use them too much. Why can't apple see that and just give us a real battery?!
How is thinner or lighter more fragile? I've never seen a phone bent and dropping a thinner phone vs. a thicker phone has no difference on the outcome. Plastic vs. metal does make a difference.
You're asking a sports car maker to re-engineer their vehicle to give you a bigger gas tank because you love driving the car so much but there is much more involved. If driving long distances is so important to you maybe you should drive differently or drive a different car.