From a customer perspective, there may be two OSs - that's really a marketing question. From a developer perspective, I expect them to arrive at one API, with

From a customer perspective, there may be two OSs - that's really a marketing question. From a developer perspective, I expect them to arrive at one API, with a few options to allow feedback from various sources (tap or click), and handling multiple screen sizes gracefully, and therefore pretty much one OS, so that you can build one app across devices - this is exactly what they are trying out with their ios app port. Once you do that, it doesn't make sense to have two APIs. I can't think of many features that would be exclusive - to take your example of energy budgets, saving energy on both is equally important now that laptops are a mainstay and desktops an afterthought. We may well see ARM laptops for this reason. Watches are the one exception that have a budget so tight at present that normal apps just aren't feasible. So I think a merge is exactly what is on the cards in the long term, particularly as they are now run by an operations person and the money flows in more and more from phones, not computers.