Well, force touch.
Anything new on hardware could be claimed as "current-version-only".
Luckily, if the only brand new hardware added on iPhone 6s or 6s Plus is force touch screen, I think I don't need to expect much difference between current 6 and upcoming 6s.
i think something will be a signifier that you have the S model. with the 5S they had an aesthetic departure and i imagine apple appreciated this: it helped those with a fixation on 'status' feel like everyone knew they had the latest model. if apple makes the 6S visually identical to the 6 it will surprise me greatly.
Fully cloud based thing? Where are those apps?
And if my device heavily relies on Internet, I would better not buying it. Chromebook is an example moving ahead of time. They have too much faith on their cloud storage service security.
i did say 'one day' - and i doubt apple would do it the way google does, but really, this would just be an option for those who don't mind relying on connectivity. i'm sure they're out there