Having spent time with an S4 I can say fitting something that size in your average pocket isn't a problem, well it wasn't for me. So for me a 4.8" iPhone sounds very nice.
One handed use on the S4 wasn't a problem either, and I don't have big hands. But I can also see how some people with smaller hands, like my fiancee, would have a bit of trouble with one handed use. Catering to everyones liking will never be possible.
Not sure if they will keep the 3.5" model if they do release a bigger i6, but I'd imagine they'd keep the 4" as the alternative to the larger phone.
Time will tell.
One handed use on the S4 wasn't a problem either, and I don't have big hands. But I can also see how some people with smaller hands, like my fiancee, would have a bit of trouble with one handed use. Catering to everyones liking will never be possible.
Not sure if they will keep the 3.5" model if they do release a bigger i6, but I'd imagine they'd keep the 4" as the alternative to the larger phone.
Time will tell.