Personally, I believe it will be nothing but a 4S which is still a very hefty innards upgrade.
Apple's strategy seems to be to innovate and come up with something new, be ahead of the game for a couple years because no one can match the price/cool factor, then eventually once it becomes a big orgy with hundreds of players and dirt cheap products they go on 'maintenance release', keep the high prices, get slammed by fanboys of the opposite phonesex, and come out with something new and amazing no one else can match yet.
It started with the iPod, jumped to the iPhone, then to the iPad, I predict after that it will either be TVs or ultra-thin laptops of all varieties.