I think your right, next years 6c will inherit the current 5s specs. But I bet the new iPhone 6 will have some amazing new features which will push me to the new designed 6. If they go with a larger screen I may have to go with the new 6c next year and just forget the cool new features.
I would also bet the next iPhone will have more rounded sides, and maybe they will skip the aluminum altogether since so many people are digging the the Plastic ones, or some new material which would be cool.