When I say arm will win in the long run, I don't mean that WoA will have anything to do with it. WoA as it exists today will likely be abandoned.
I do think in the next decade Microsoft will focus on creating a full abstraction layer so it's software can run on any HW. This would be a longterm play. At launch, Would it be feature parity with what exists today...no. but over time it will build up the codebade, drivers, etc. To over take the current windows ecosystem.