All the things people have suggested in this thread (and others) aren't really going to reinvent the iPhone. A new design on the iPhone 7 will reinvigorate sales no end as all the people on the iPhone 6 will come off contract (the last generation of 2 year contracts). I think we're now in the position where computers were in 7-8 years ago. Even though phones are getting faster, there isn't the pressing need to upgrade like there was before. The iPhone 6s is a tremendous technical achievement in terms of the A9 chip and 3D Touch (not to mention the 2 GB ram everyone has been asking for) yet people don't seem interested and even on this techie forum there are plenty of people intent on keeping their iPhone 6.
I'm wondering if the iPhone may follow the iPad onto an 18 month release schedule. This would give Apple an extra 6 months to get a new design perfected which would avoid things like antennagate, scuffgate and bendgate effectively combining the new design that people want with the maturity that comes from an s model. It would also give a longer iOS development time (or untie iOS releases from having to match iPhone releases).
Besides this, they really need to sort out the iPad once and for all on the software side. If they are pushing it as the future of computing then it needs an OS to match rather than a simple scaled up phone UI. This is what the iPad needs - the proposed Air 3 only seems to feature extra speakers, a flash and A9 chip (if not an A9X then it probably wouldn't be that much quicker than the A8X) a how many people would upgrade their iPad for that?
The AppleTV, despite looking like last year's hardware, seems to have largely unfinished software that really lacks the Apple polish (the way the app name/film title etc appears on the screen when you select something is appalling) and was clearly unfinished - no API for Siri searching of 3rd party apps, Computers content appearing in search (not just ripped content, but items previously purchased from iTunes) and mandatory Siri remote control for games. This adds to the issues with the watch (underpowered, pointless apps, poor battery).
So, in summary Apple will probably be ok in 2016 with a new design of iPhone, but they will need to do something special for the follow-up. Without a revolution in iPad UI and software features or a way of making the watch more useful/indispensable to the masses those products will continue to suffer. Apple TV can be salvaged with some good software updates in the next few months and the Macs will no doubt gain more traction with new rMB-esque design cues for Skylake.