How do you know that AMD does not run its own version of ME?
The only viable solution I see is open hardware.
Mitigation does not necessarily mean to entirely protect. Having less of a homogeneous ecosystem mitigates the risk of any one vulnerability, as it's unlikely to affect as many systems. It's not a solution, but it may help.
What does viable mean? Where can I go out and purchase it? Yes, hypothetically, anything is possible.