So Apple will unveil 3 iPhones in September? i think it's more possible that they will reveal the iPhone 7 4.7" and call the 5.5" the iPhone 7 Pro (or iPhone Pro). if what's added is the dual camera it makes more sense to do that with the 5.5" than it does creating a separate phone just for the dual camera feature.
I'm also not convinced we will see the smart connector on the iPhone.
I don't think there will be 3 phones. I think Apple is going to pull the same trick they did with the iPad Pro. They're going to introduce the "7 Pro" in place of the "Plus" which then becomes last years big phone. I think they've decided they like "Pro" better than "Plus" as a naming convention. And, that way they can maybe charge more for what would have been the Plus model. Just like they seem to be depreciating the "Air". I wouldn't be surprised then to see a 4" 7 come out that is essentially unbranded, letting the size do all the talking for them -- the iPhone in two sizes: 4" & 4.7" and the iPhone Pro.
The Smart Connector makes too much sense not to implement, if for no other reason than to tap into battery packs. But if the headphone jack rumor is true, that connector will go a long way toward making integrated adapter cases too, which may mean the difference to retaining many iPhone customers or not.