Microsoft only licenses Windows 10 on ARM to PC makers to preinstall on new hardware, and the company hasn't made copies of the operating system available for anyone to license or freely install. By switching to ARM-based machines, Apple might not be ruling out Bootcamp, Parallels, etc., but it is significantly reduce the number of available apps available on either operating system. ARM CPUs process instructions differently from x86 CPUs (made by Intel and AMD) so any specific app has to be written for ARM in order to function. This will hurt people who rely on specific apps (either MacOS or Windows) until/unless the vendors for those apps release updates that support ARM.
On John Gruber's WWDC Talk Show, Craig Federighi confirmed that Apple would not support Boot Camp on ARM Macs: "We're not direct booting an alternate operating system. Purely virtualization is the route. These hypervisors can be very efficient, so the need to direct boot shouldn't really be the concern."
Apple demonstrated Parallels Desktop running Linux in a virtual machine, but there was no mention of Windows support. VMWare has asked its community about how they would use its Fusion virtualization on ARM-based Macs, but there’s no commitment to building the app just yet.