What makes general OS difficult on a SoC is usually the lack of hardware virtual<->real RAM address translation accelerator, the MMU.

I guess it's not that important if developers had no raw pointer access so that object can be anywhere dynamically assigned(Java!!! also JavaScript and all interpreted langs). But basically all desktop OS apps are written in C and they always want single consistent virtual addresses to jump around in and none of apps work without the hardware dynamic translation.

C semantics account for segmented storage, that is why two pointers holding the same bitwise address are not considered to point to the same object, when they are derived differently.