At the end of the day, its all about awesome games and in my opinion the kinect doesn't really add much to that unless its some sort of family type party game. Now I do like the convenience of the kinect(voice controls) in some instances like walking into my den and simply saying "xbox on" and it turns on my xbox and my tv and then the kinect camera recognizes me and signs me in automatically. I also like the fact that if something bad ass happens during gameplay, I can say "xbox record that" and it automatically saves the last 30 seconds of gameplay.
But when it comes to console gaming its all about giving the people what they want and if the devs want to make money they will also give the people what they want or make something so cool that the people will want it. If microsoft made it optional in the first place, they would have sold a lot more consoles than they have so far and at the same time I am sure they would still have a decent attachment rate for the new kinect. I bought two xbox one's on release day and if the kinect where optional I would have probably bought them anyway but at least I had the option to and not be forced to. If devs wanted to make a game with kinect integration they can simply make it clear that kinect will be requried to play the game and if the game is in fact that awesome then you will see kinect sales increase.