A significant but unpredictable factor in this question is the involvement of the US and EU governments in anticompetitive actions. Google has finally found the eye of the US government on them; they were denied a seemingly innocuous deal with Yahoo and ever since have been reeling in the awareness of their own vulnerability. Both Apple and Google are susceptible to this kind of intervention at the moment, and i think how, when and if that actually occurs will have a big influence on their mobile OS's trajectory.