Given how utterly trivial it is to accidentally achieve turing completeness, I suspect any reasonable subset you could come up with would also be capable of gen

Given how utterly trivial it is to accidentally achieve turing completeness, I suspect any reasonable subset you could come up with would also be capable of general computation. Moreover, such a design would be inherently expensive and inefficient, because it can't achieve the economies of scale modern uCs do, nor can it do anything without an external (presumably networked) command for every single operation.