I hope the 4s runs 7. That would be greatly disappointing.
I'm pretty sure it will not only be on the 4S, but it won't lack any features. The 4S is still powerful enough that it will be able to run any feature of iOS7.
iOS 7 will be released with several new features, one of them is a fresh new designed UI exclusively available for the iPhone 5 and the upcoming iPhone 5S only.
I hope they don't do something like that lol.