I think the key lesson of things like Fitbit's smart watch has been that you don't get a good watch by taking "everything it could do" and then subtracting feat

I think the key lesson of things like Fitbit's smart watch has been that you don't get a good watch by taking "everything it could do" and then subtracting features until you get where you want to be. You do it by building up features from user story primatives (e.g. I want to glance down and see who's calling). Then shipping with enough primatives covered to be useful.