One thing to keep in mind is that Imperial laws (i.e. laws in the Imperium
1) are not necessarily
Imperial laws (promulgated by the Imperium). I think that Imperial laws
2 tend to be as minimalist as they can be and still cover 300 subsectors. There are a few basic laws that covers everybody. Some of them deals with rights accorded by the Imperium to sapient lifeforms. Cleon I specifically excluded robots on the grounds that while some of them might arguably be sapient
3, they are provably not lifeforms.
1 Which I will henceforth refer to as planetary laws to avoid confusion.
2 Promulgated by the Imperium.
1 Turns out they weren't back in his day (TL12).
I don't see any reason why the Imperium should consider human brains to not be lifeforms. It could, of course, but we have no evidence (either way) that it does.
Individual member worlds, OTOH, could (and I'm sure some would) define cyborgs as non-persons. This allows a much greater freedom in developing individual worlds. We are barred from having Imperial member worlds governed by psionic elites because canon tell us that the Imperium itself bans psionics. I see no reason to bar ourselves from having Imperial worlds with rampant cyborgism
as well as Imperial worlds with cyborg slavery.
YMMV.
Hans