Despite the larger screens and the higher chance of the phone getting bent (look again at the bendgate controversy), a more SEO centered question would be focused on marketing. Will the iPhone and iPhone 6 Plus help relieve some users of the challenges that come along with shopping on a smartphone? If so, will mobile conversion rates really begin climbing?
Mark Ballard has a post on Search Engine Land that discuses the issue of whether or not the larger iPhone 6 screens will be able to close the gap between desktop conversions and mobile conversions.
You can find the link here: Are Bigger iPhones Better For Paid Search?