I could see some people wanting the 4" screen size. But the 3.5"? Nope. To cramped and small. Just look at how iOS 8 and iOS 9 run on a 3.5" device. The keyboard takes up more than half the screen. The 4" size is the smallest that iOS runs nicely on
If Apple doesn't at least bring back the 4" size I will be forced to buy a 5s when my 5 dies. I hate buying old equipment but I cannot hold the 6s in one hand and feel comfortable. I bought both my boys 6's and have tried them out only to miss my 5 even more.
I just hope if Apple does bring back the 4" screen size they include force touch.
Cheers.