Without knowing the inner workings of Apple's scheduler: I don't think there is any reasons this wouldn't work on x86 hardware. All you need is some API to tell the scheduler whether a task should be done "asap" or "whenever".

But you then get a huge tradeoff: If you reserve over 50% of the computational power for "asap" stuff, then all the "whenever" stuff will take twice as long as usual (assuming the tasks to be limited by compute power). On a 8C Intel that means that, for a lot of stuff, you're now essentially running on a 4C Intel. Given the price of these chips that MIGHT be a difficult sell, even for Apple. On the M1 they don't seem to care.