I would like to see more 4.5" phones.
Even if there are reasons to have phones smaller and larger than that, I really think 4.5" is the sweet spot, so long as the body of the phone isn't significantly larger than the display.
Plenty of people prefer using phablets or small phones (I've got by on the 2.6" display of the Kin One for a few months just fine), but I think the industry will settle on 4.3 to 4.7" for the majority (51%+) of smartphones.
My main, current phone is the HTC One. I think the display is slightly too large at 4.7". It's not uncomfortable to use, but it's less strain on the thumb to use a slightly smaller display when I'm just using one hand. Which is most of the time, since I'm usually just picking up my phone while at my desk, while walking, before setting off to/from work, etc and not using my phone like a tablet.
And I don't have dainty hands, so I would bet that 4.7" for the display alone is a little big for a lot of people, let alone 5.9" displays. The physical phone being larger isn't a problem, it's more the range of motion from end-to-end on the touchscreen that makes it a stretch (literally) to use with one-hand. So long as smartphones are still phones as well as everything else, they should be optimized for one-handed use. I don't plan on holding up the 7" or 8" tablets to my head.
I don't like the move to 6" phones personally any more than the race in the dumbphone market to tiny phones. I remember everyone use to joke about how we would end up using thimble sized phones, but the market pulled away from that before PDAs finally converged with phones.
I'll gladly take larger screens on tablets, but I just don't something in between a smartphone and tablet. If you like having phones the size of the Notes, Mega, One Max, etc, that's fine and good for you, but the phone manufacturers aren't getting any money from me for those phones.