Thanks to you and @kingosticks above for digging up these official accounts.
Cursory examination of rpi firmware suggests that this DRM logic is implemented in start.elf, one of the proprietary blobs required to boot an rpi. This is, in itself, significant, since opening this blob would obviously make this restriction easy to circumvent. In other words, rpi have taken design decisions which essentially motivate them not to open up these boot blobs, but rather use them as a chokepoint of control over the platform, see also [1].
From this, we can infer that rpi.org will probably never get rid of these boot blobs (as opposed to simply not having found the time/resources to do something about them).