I think the 4.3" is kind of like the goldilocks zone for screen sizes right now. With a range of 3.7"-5.3" out there, 4.3" seems like a conservative compromize. My current DInc2 with it's 4" has been a wonderful step up from the Eris and it's 3.2" but I think I'm ready for another small step up.
It is hard to go back down in size once you're used to something, so I think it prudent as an individual to make small steps up instead of leaping to a 4.7 screen.
Of course it is a very individualized preference and to each their own, but I am hopeful that this 4.3 speculation is correct