Hypothetical scenario:

User pays the initial cost of engagement - Atleast 2 seconds to unlock the phone. After that, all actions user performs are in the "Engaged State".

Imagine if you have to press a button every 3 mins but you have to pay the 2 second cost of unlocking the phone, searching for the button(which can be memorized) and then getting visual/sound feedback.

Compare this with a Remote Control that is sitting on the table. Pressing a button on it every 3 mins has lower impedance.

The examples you're citing have a fixed 2 second "initialization" cost and then phones are fine as long as you're engaged in a session. All feedback is visual (and sometimes audible). Soli is far inferior to a phone in UX because it literally has no feedback besides "hoping" your gesture would get recognized. Moving hands in air has substantially higher ambiguity than touching your phone in "engaged session" mode.

On my current phone I don't have to unlock it to do media controls. I'm not sure why you'd expect anything different with Soli. Also from what I'm aware of, the phone unlocks extremely quickly. Reporters saying (partially because of Soli) that they barely see the lockscreen if picking up the phone.

Good thought experiment, though I do think Soli still makes sense. There is no reason Soli doesn't work exactly the same as a remote - there is no need to unlock the phone if the chip is always on, and can even detect when a user is engaged prior to an action.

In my mind the only difference between a button on a remote and a "button" that sits in the air above my coffee table is reliability, which will be solved in the future. I know pressing button x does y, it makes equal sense that moving my hand like x does y. Feedback could be anything from a puff of air, tiny light flash, small 'ding' sound, etc.

Sound is OK for a feedback of success. What we also need is visible affordances -- signals of what can be done, when, where, and how. Also, what I hate the most with these gestures is fearing that I'll get it close but not quite, and something else (or nothing) will happen. With a button, you can feel it and immediately make micro-adjustments while pressing to ensure success. This can possibly be done with sound, but I haven't seen it done well, yet...

Agreed - but those are software problems that can be solved with training or good ux. iPhone has no indication of what can be down (How do you know you can swipe your homescreen up, down, left, and right?). Discover-ability is a challenge that has been overcome previously and can be overcome again.

Part of that is the two games on the announcement page which show you examples of gestures. Doing gesture x accomplished y in the game, so maybe in the next app you open doing gesture x will accomplish something.

Your comment reminds of “Design for everyday things” book. He talks about Affordances and Signals.

I agree with you, sound can be ok as a signal that something has happened. It is fine with some users, but annoys others (beeps when a camera auto focuses, always a split opinion. Some people like it and some don’t).