Aw. Apple Watch looks a lot like the Watch icon (shown when the system was busy) in the original MacOS.
Now if someone can figure out how to do pointing on a tiny screen, it might work. Maybe you wave you arm around in space and the accelerometers drive the cursor.
Now here's a thought. Wear two devices, one for the screen and one for pointing. Move the other hand around to move the cursor. Or track the other hand when some distance from the screen when you need a cursor smaller than your thumb.
We're going to need that technology soon, so you can do stuff while wearing VR goggles. So downsize it to the wrist.
Now if someone can figure out how to do pointing on a tiny screen, it might work. Maybe you wave you arm around in space and the accelerometers drive the cursor.