I hope the button is depressed and concave (like the old home button), otherwise there will be occasional accidental presses, just as there are now with the current iPhone, which depending on the action assigned, could be disastrous. The Watch Ultra action button is partially depressed and concave, but I think on a phone, it would have to be more since a phone is handled and has objects pressed against it in pockets and purses constantly.
Assuming it’s designed with that in mind—
Single: camera picture mode
Double: camera video mode
Triple: maybe lock/unlock car (if within certain range)
Long: maybe open all windows in car (if within certain range)
Side note- I can never get to the camera fast enough. With the current swipe from Lock Screen method, I often end up swiping away notifications instead. And once in the camera app, I’m often fumbling trying to get to video mode. And often by then, the moment I wanted to capture has passed.