Why a watch? Why (ear/head)phones? Why a phone in the first place?

Rumors are that Apple is working on VR Glove & AR glasses.

They're taking things that people use every day and cramming as much functionality into software as their hardware will allow.

Sort of joking sort of not: Eventually there will people wearing full sets of Apple accessories, getting into their Apple car, driving to an Apple home... And all the technology will be seamless (or as seamless as they can make it based on their current track record.)