Just drop the price with Kinect to $399, eat the losses and totally dominate the US market share.
Even at $399 they wouldn't dominate the US market. For one, Sony has made a lot of new fans (or maybe more accurately, won them back) because of their stance against DRM from the start. And some that are going to buy a One are still saying they are buying a PS4, first, then a One. Finally, and quite importantly, MS is going to be having supply issues for at least the first 6 months, if not more. Sony, on the other hand, are going to be pumping plenty of PS4's into the marketplace. For many who want a next gen system in the first 6 months - 1 year, the PS4 and Wii U are most likely going to be their only options.