Open standards adopted by the internet and mobile devices and the have made it highly unlikely that any OS could every achieve the level of lock in that made Windows what it was.
If you send me a mail you don't know where I'll be or what sort of machine I'll be using when I open it. If you write a blog post you don't want to have to care what browser I'll use.
Sure there's a base level of functionality that any OS will need to provide to be a workable computing device (mail, web, maybe the ability to at least view PDF and Office-type documents, that sort of thing) but there are already dozens of OSes providing that and it feels unlikely that there could ever be anything big enough to move us all back to a single platform.
