Sure, of course they want to minimize fragmentation. But developers have been making apps for the 3.5" (3:2) form factor since 2008. So continuing to make a 3.5

Sure, of course they want to minimize fragmentation. But developers have been making apps for the 3.5" (3:2) form factor since 2008. So continuing to make a 3.5" (3:2) phone alongside a 5" phone (either 3:2 or 16:9 or anything else) wouldn't make any more work for developers than they've already made.