The new rival is Tizen, basically the Linux kernel plus the WebKit runtime. Tizen is supported by Intel plus Samsung.
This undoubtedly presages the nature of the software wars of the future. They will not be Apple versus Microsoft, or Microsoft versus Google, etc. They will be struggles between different versions of Linux.
Not at all. Android already dominates in mobile. The only real contender, iOS, is fading. WP has no chance. W8 is not a factor in mobile, and is not likely to become one. So what is the prospect? When another version of Linux turns up, under the stewardship of the current hardware leader Samsung, there could be a serious contest for dominance between the two versions of Linux.