What Apple needs to get right with its new iPhone 6S and 6S Plus

New iPhones are expected at Apple's 9 September event, but as the competition improves and phones last longer the next upgrade has its work cut out for it

Apple is expected to launch a pair of new iPhones at its 9 September event in San Francisco, and along with it a renewed push for its Siri and HomeKit features.

But if Apple intends its devices to become the central hubs of people's connected homes, or even just to persuade customers to upgrade, what does the company need to get right with its iPhone 6s and 6s Plus?