IT'S A smartPHONE... ...what happened to smaller being better?
I suspect for many, the "phone" portion is like the "tunes" portion of iTunes. Yes, it is also a phone but the majority-to-vast-majority of the time, this "phone" is used as a portable computer for non-phone tasks. And even when it is used as a phone, I'd personally separate out voice from texting. In my own case, I find it easier to text on an iPad mini right now as the iPhone's keyboard- even in landscape- is just too little for me. I hardly ever use the "phone" functions for actual voice calls.
So, for those that really use the voice portion of the "phone" functionality a lot, I can easily see an argument for an iPhone mini. Maybe the fabled "iWatch" will hit that target? However, for the rest, I suspect that even if Apple rolled out a 6 at 5.5, 4.7, 4 and 3.5- all at the same time and in good enough supply so that anyone wanting any of them could get it- they'd probably sell in volume in that order (most at 5.5, next most at 4.7 and so on).
Personally, I bet a lot of iPhone defectors and a lot of Android only smart phone users envious of iOS breadth & depth will come running to the bigger screen iPhones. I also bet that a whole bunch of people that gripe about 4" being perfection and the larger size being "stupid", "can't fit my pants pockets", et all will be in the "shut up and take my money" fervor after Apple rolls them out and then they'll be posting gushing love for their new bigger-screened iPhone post launch. Those with any integrity might post something like "but when I actually saw one…" and similar but many will just shift as soon as Apple formally endorses the new sizes with the launch show… as if they never said a negative word about bigger screens pre-launch.
This all reminds me of the massive spin of negative arguments when there wasn't an iSight camera in iPad 1 ("why does anyone need a front facing camera in an iPad", "why would anyone want to look up at my nose hairs in video chat", "how would one ever stabilize the iPad enough to use video chat?")… that flipped to gushing love about the incredible "FaceTime" upgrade in iPad 2. Or how "720p was good enough" before there was an

TV3 but then all of that pile of supporting argument seemed to evaporate overnight when Apple rolled out 1080p

TV3. There's so much "whatever Apple says" following which, right now, clings to what Apple has available right now. However, as soon as Apple shifts and spins 4.7" and 5.5" as magical/wonderful/etc, the vast majority of this crowd will shift right with them. It's all "stupid", "an abomination", "need new pants" before Apple speaks but Apple is never "stupid", "releasing that abomination", "pants magically adjusted" afterwards. Instead, all of these negative arguments against bigger iPhones will just evaporate right at launch and many of the most passionate posters of them will flip that passion to supporting the amazing, magical, new bigger-screened iPhones. Over and over and over.