Doubt there will be a redesign for the next iPhone. As others have said, this current one is a major redesign and if Apple continues their trend, the next model will be the 5S and the design will be pretty much identical to the iPhone 5.
However, the overall shape of the iPhone 5 is borrowed heavily from that of the 4/4S. In this respect, the iPhone 5 evolves from 4/4S, which does not deny the redesign.
Much the same way how the overall shape of the iPhone 3G/3GS is borrowed heavily from that of the original iPhone, and nobody denies the 3G/3GS is a redesign. Same chrome border and rounded design, but the 3G/3GS is fatter with plastic backing. The iPhone 5 has the same stainless steel band and squarish design seen on the 4/4S, but it's thinner as a unibody with metal backing.
Much the same way how the overall shape of the iPhone 3G/3GS is borrowed heavily from that of the original iPhone, and nobody denies the 3G/3GS is a redesign. Same chrome border and rounded design, but the 3G/3GS is fatter with plastic backing. The iPhone 5 has the same stainless steel band and squarish design seen on the 4/4S, but it's thinner as a unibody with metal backing.
I've been saying this for years! Once in a case, ALL the iPhones look pretty much the same.
Imagine a group of people in a restaurant, with their phones on the table. There's no way of quickly seeing a difference between a 4 and 4S and the only thing one would notice about the 5 is that it's a bit taller.
Apple have done nothing but tweak the basic design since day 1.