Realistically iOS 8 before we see any major changes.
Actually I think we will see a major change in iOS 7 or iOS 9... Reason for this is, iPhone "6" is released on iOS 8 and the "5S" on iOS 7, they would want to give people a great reason to buy the new iPhone if it looks the same and only has internal updates, they would want the new iOS to make it the selling point (even though you can just update, for some people it makes a difference and they know that)... Whether you are right or I am, I just hope the new iOS will be worth the wait. I love iPhone, but who says a nice refresh to the software wont be bad.