The hardware for the bigger screen size is the easy part. Android makers already prove the point. It is the apps that is difficult to deal with. Unless Apple find a way to do more that auto scaling, a standard Iphone app will look pretty bad on a 4.8 inches phone. The innovation has to come from the software size to make it happen..
Same go for NFC. Unless Apple find a way to use NFC in a big way (e.g. roll out a payment systems using NFC with Visa,Mastercard etc.). As of now, NFC is more or less a toy for 90% of people who get them (yes, hear about using NFC and tag to turn on the volume, changing the setting etc..). It need to be used by the non-tech guy easily.
It is almost a guarantee that Apple will have to launch something in 2Q13 time frame. If you look at the sales in 2012, there is a distinct pattern of boom an

d bust. The fast rollout that Tim Cook talked about in Iphone 5 launch has a very major consequence on the sales of the device. Iphone 5 is going to be very front loaded (i.e. 4Q12 and 1Q13 will sales majority of the Iphone 5). The manufacturing line and suppliers will all idle in 2Q13 on waiting for the next Iphone release. It make sense for Apple to speed up the cycle and smooth out the sales. IGZO with longer battery life is a good enough reason for 5S.