Instead, I think the answer is now apparent, with the new product introductions of the Tim Cook era - Apple Watch, AirPods, and the forthcoming HomePod. These interconnected "smart" devices are all relatively inexpensive (as far as Apple products go). Interactions are largely through voice, or a few taps. You forget you're wearing the Watch or AirPods, and the HomePod looks pretty unobtrusive.
A smartphone is pretty much required to use any of these devices today, but you can imagine that won't always be the case (recall the iPhone required a Mac or PC running iTunes, in its early years).
While none of these devices are essential now, when you need them they're really nice to have handy. They're definite improvements on dumb watches, dumb speakers and regular headphones. I already use my Watch to pay for coffee and taxis, respond to texts, and in the years to come it will probably assume more of my phone's role. The HomePod right now is limited to music, HomeKit, and simple cloud queries, but it seems a safe bet that in the years to come its capabilities will grow (merging with or running Apple TV, serving as a phone, sending and relaying messages to contacts, etc).
Macs will continue to be around, for "serious" work (though they've made up a tiny fraction of Apple's revenue and profits and that seems unlikely to change). Other screened devices, like iPads and TVs, will be around for play, photos and short written notes. If there's one element missing it might be a standalone TouchID keyboard. But more of our future, I think, has come into view this week - and it's mostly screenless, distributed between wearables and innocuous furnishings like the HomePod.