In terms of naming, calling it the "iPhone 4S" makes no sense in my opinion.
The second generation iPhone was allowed to have "3G" in it because of the 3G capabilities. The iPhone that followed couldn't be called "iPhone 4" because it was the 3rd iPhone, and it couldn't be called the "iPhone 3" because it would be confused with "3G". So adding the "s" to it made sense because it then allowed the numbers to match up the version of iPhone they corresponded to, and in terms of marketing consumers would eat up the "s" that referred to "speed."
The iPhone 4 made sense, it was the fourth generation iPhone. If they name the next iPhone with "4S" it won't make sense to me because the iPhone 4 is already quicker than the 3GS that already refers to speed. And then the iPhone following it would be the sixth iPhone and I don't know if they'd just skip the "iPhone 5" name and go to 6. It just doesn't make sense. Also it would be better to market it as iPhone 5 with A5 chip and iOS 5.
I'm thinking that they just ultimately have to drop the numbers soon and simply refer to it as the "New iPhone", because how ridiculous is it going to sound referring to your iPhone with such large numbers?