Any idea on how people will virtualise Windows? Only with Windows 10 ARM version I suppose?
Yeah, Windows for ARM is the only feasible approach to virtualizing Windows. If you're not familiar with Windows for ARM, though, it's not really very useful. It's a languishing and stagnant platform that isn't seeing much love or attention from Microsoft currently. That could change, depending on Microsoft's future platform strategies, but for now it's not likely to be a satisfying or performant solution for Mac users who will continue to need Windows compatibility in a post-Intel landscape.
More broadly, I expect QEMU to provide a technically functional solution, but as with all forms of cross-architecture it's unrealistic to expect good performance. I don't think it will take too long before you can fire up an emulated x86/Windows environment via QEMU but I doubt that will ever be a solution you'd want to rely on for day-to-day tasks. Sufficient for one-off or irregular tasks though that aren't very demanding.
It's possible that Apple include some assistive functions in their custom ARM silicon to make a QEMU-style emulation more practical, but I wouldn't bet my workflow on that. Even in the best possible case scenario it's never going to achieve virtualization-level performance or reliability.