A fancy watch like the Apple watch or a luxury watch I wouldn't wear that way, but a rugged Casio I might. And I can see how the Op might while diving for utility and safety purposes.
You obviously were not a fan of Kris Kross back in the day.
And the demo watches won't activate from sleep with motion. So I guess we wait until a reviewer video or launch day to see if the watch will wake from sleep while being worn underside.