There has been the protruding lens and the much bigger battery, both of which are dismissed because the argument "no parts leaks" loses most of its punch if there's even one part(s) leak. Better to ignore those or spin them as being only for prototypes or other Apple hardware than have to lose the strength of that punch.
There's also very credible references to 5.5" iPhones offered by WSJ and Bloomberg but, of course, in this particular instance, they "don't know what they're talking about". However, any references to iWatch in spite of nary a single part leak is generally met with full expectations of an iWatch. So apparently, only THIS rumored product can't exist.
Again, I go to the money argument. Deliver both sizes to fully compete with the most tangible feature (or benefit) of the Android smart phones. That would make it possible for anyone who desires a bigger screen enough to buy Android to now have a genuine alternative that runs iOS. Bite into that market at only 4.7" and Apple probably leaves the >5" screen buyers to continue giving their money to competitors like Samsung for up to another year. Why do that?
In the Samsung trial, Apple documents made it clear that Apple believes the market has moved on to bigger screen phones (that's why Apple is abandoning the previously spun "perfect" sizes of 3.5" and then 4"). And the gist of the financial remedy was "lost sales" due to Samsung wooing would-be iPhone buyers away with their bigger screen phones. If Apple believes what it shared in court, it only makes sense to roll out something toward 5" and something toward 6" so that there is an iOS something to appeal to ALL that business lost to Samsung and other Android phones.
"We" see 4.7" as a big increase and 5.5" as HUGE because we are accustomed to 4" iPhones. But the big-screen Android crowd has seen phones with screens bigger than 6". To them, 5.5" might be close enough to compromise some size to get iOS, while 4.7" might be "too small". Apple knows it will sell "us" whatever Apple rolls out. I think a 5.5" is about wooing the Android crowd (though some of us will be happy to go 5.5" too).
A highly revolutionary (complete) design change of the Mac Pro had it's first rumor hit only 5 days before Apple revealed it to the public. Relative to it's predecessor design, that change was MASSIVE and yet, not a rumor and not a part until 5 days before it was revealed. A 5.5" iPhone is a screen .8" bigger than a 4.7" iPhone with nearly everything else likely to be the same or close to it.
And OP, no rumors are definitive. While the rumors have piled up that a bigger-screened iPhone is impending, until Apple takes the stage and rolls them out, anything can happen. If you want definitive, you have to get the word straight from Apple. If you want "maybe", "probably" or perhaps "likely", an increasing pile of rumors may imply what is going to happen.