You're basically patching the hardware to work with immutable software (as you won't have the windows sources). At the same time, the QEMU ARM virtual system and the Microsoft designated ARM SoCs are perhaps closely compatible whereas it would be very different with other ARM implementations.

Only GIC (interrupt controller) bugs needed to be fixed. The GIC is standard since the Cortex A9. On the A9, you have to use an HAL extension (declared in ACPI) for the timer(a sample is available on MS' Git repo). On the A7/A15 and later, Windows uses the GTDT ACPI table only, so nothing is needed :)