Then there's the question of pent-up demand for a larger iPhone. It's hard to pinpoint how many iPhone owners have avoided upgrading because they want a bigger phone, or how many big-phone aficionados would switch from Android to iOS if they had the option. (Some iPhone customers still insist that size is not that important.)
We do, however, have market share and growth data to lend perspective. According to Canalys, 34 percent of phones shipped in Q1 2014 had screens 5 inches or larger. Perhaps more important, that segment grew 369 percent over the same quarter a year earlier, faster than any other size category. All of that, combined with the iPhone's perennially strong customer satisfaction numbers, suggest that Apple should gain market share with larger offerings.
Which brings us to China. The market for larger phones is especially robust there, in Apple's most prized growth market. Apple also happens to be enjoying a banner year in China. Not only has the company signed China Mobile, the nation's largest carrier, but it has also managed to rein in the grey market where iPhones sold without Apple maximizing its profit. Finally, China has its own dynamic of shifting subsidies. Chinese government regulators are reported to have instructed carriers to cut back on subsidizing smartphones. The main likely effect of that? It will shift sales to cheaper, homegrown brands like Lenovo and Xiaomi.
But don't be surprised to see a secondary, opposite effect: Higher-priced phones from premium brands (Apple, mainly) could reassert themselves among wealthier consumers as a status symbol. It arguably carries more cachet to be seen with an iPhone when fewer of your peers can afford one.
—By CNBC's Jon Fortt