Yes, the Raptor Computing POWER systems are almost entirely open. The CPU is entirely open, save the die mask. It's worrying that these vulnerabilities are not

Yes, the Raptor Computing POWER systems are almost entirely open. The CPU is entirely open, save the die mask. It's worrying that these vulnerabilities are not disclosed in a way that lets people take control of their devices. That the ME is so tightly integrated seems mainly to be for cost savings. There is also an argument for increased security, as now your attacker must be able to work with a decapped highly integrated CPU. Intel did at one point do what you were suggesting -- if you look at the sandsifter project the author found a family of devices that had a parallel execution unit that was dispatched instructions with a "secret" prefix that had full access to memory. This could still exist in newer processors but be better hidden, it would certainly make a lot of one might want to do with the ME a lot easier.