iPhone 6s: Will Sales Fall Short Of Expectations?iPhone 6s: Will Sales Fall Short Of Expectations?

iPhone 6s: 9 Features On Our Wishlist

The addition of new features like Force Touch, an upgraded processor, and a better camera will represent a modest upgrade to the 6 and 6 Plus. These features suggest that this year's smartphone refresh will pale in comparison to last year's iPhone 6 upgrade, according to a report from John Butler, a senior analyst with Bloomberg Intelligence.

The Aug. 27 report also notes that the iPhone 6s and the iPhone 6s Plus will have a tough road ahead, due to the success of the iPhone 6.

Specifically, Butler draws attention to a forecast by IDC (full report by purchase only) that Apple would ship 232.7 million iPhones in fiscal 2016, compared with 233.8 million in 2015. This projection would mark the first-ever year-over-year decline in iPhone shipments, if the forecast proves accurate.

"Apple will face tough sales comparisons in the next year, given the strength of the last upgrade cycle, a challenge that may prove too difficult to overcome," Butler wrote in the report (not available online).

Still, the report notes that with Apple's iPhone refresh, which will be part of a major media even the company is planning on Sept. 9, Apple can tap the upgrade opportunity that exists with users still on older-generation iPhones.

"This may help to partly offset the tough comparisons posed by the outsized success of the iPhone 6," the report noted.

Butler also suggested that Apple's return to a 4-inch model of the iPhone could prove alluring to consumers who don't want or need a large smartphone. The company's current most affordable iteration -- the iPhone 5c -- does feature a 4-inch screen.

Among the enhancements expected for the latest iPhone 6 and 6 Plus, which will likely be named the iPhone 6s, are a faster A9 processor, an improved camera, and Force Touch technology, which detects the force of a tap on a touchscreen and responds differently to variations in pressure.

"These new specs could take a slight toll on margins, though should drive upgrades and incremental sales," Butler noted in the report.

One area of the iPhone which may not be upgraded -- no doubt to the chagrin of many -- is the smartphone's battery.

With Apple's focus on making its devices thinner and lighter, particularly the iPhone, the amount of room left over for a battery has been shrinking.

[Read about problems with the iPhone 6 Plus' camera.]

A report from Chinese tech news site cnBeta indicates the new iPhone will actually come with a less powerful battery than the one found on the iPhone 6, which is an 1810 mAh battery. The iPhone 6s will reportedly carry a 1715 mAh battery, which translates to 5.3 percent less capacity.

"These aren't huge decreases, but it is of particular concern for the iPhone 6S as battery life is already one of the worst features of the iPhone 6," a report in Forbes pointed out.

In a recent column for information, Eric Zeman argued that, although the new feature sets of the iPhone 6s may be small, when they are added up the iPhone 6s could prove a much better upgrade than the previous "S" updates from years past.

Of course, no one knows what Apple will unveil until CEO Tim Cook takes the stage on Sept. 9.