Earlier quoted context omitted.
I think the official line from Microsoft would be that most software should be using .NET anyway, and in that case the same binary should Just Work on either architecture. In reality there is still a lot of native software though, so who knows how that will play out. Games in particular will always be native.
If it's like their previous ARM Windows attempt, existing native software won't work in any event because the entire platform is locked down.
Hopefully today's announcement is a turning point for that but atm windows on ARM is about on the same tier as a pre-carplay infotainment system.