NOFI, but don't be so naive ... They already require it on ARM. Chances are pretty good, if they have their way, it will be a requirement sooner rather then later. That's just how the beast works. They don't do it know, because of all the antitrust shit that will rain over them. They are hoping/guessing/betting, that in a few years, they can encourage OEM to enable it by default claiming 'see, less piratism, less virusses etc happened because of secure boot' and a few years after that, lock the platform entirely.
But you are right. We don't know for sure what will happen. For all we know Microsoft will play nice and .... right, sure it may be possible, but extremly unlikly. Embrace, Enhance and what was that last one again?