If only if Apple can squeeze the A9/2GB/64GB/12MP/TouchID/LTE/Lightning and 4" display into a 4S frame.
Considering the 4S had a 30-pin dock connector, I think this would not be a problem especially if they removed the headphone jack. The battery would probably have a lower capacity, but otherwise comperbale. The home button might have to go on the back though, and the sim might have to be non-removable. Would you use a case on this new 4S hybrid?