I haven't seen the new phone in real life but as far as I can see from the press IOS9 has introduced a context menu exclusively for 6S - but could that now have been done using the existing hardware and thus for all models? Ie. by triggering the context menu with double tap, long tap, tap and slide up or something?
But bringing pressure sensitivity back to touch screens could allow things like on-screen keyboards on tablets that allow fingers to rest on the screen without constantly registering input. Meaning that a OSK moves one step closer to a physical keyboard.
Edit:
And i just reminded myself that supposedly there is a company working on how to use static electricity to give variable surface texture. So you could perhaps recognize the location of keys by your fingers brushing over rough patches.
It is a classical critism of context menus that they are hidden and their presence needs to be learned. This problem obviously gets worse here as the context menu is only present in the latest hardware.
From a business perspective it makes sense: You are selling a package and the extra software feature is given to those pay for the update. But whether it is good design - that is another question.
And as a curiosity: Context menus are used much less in Mac OS than Windows. There is only a single button on an Apple laptop and Apple went on for decades with the one-button mouse for their desktop computers, only to introduce a multi-button mouse very late.