The ME has had many security vulnerabilities and probably more to come. For an appliance some old CPU might be good enough, but it does not get security updates. Some claim the ME might contain a NSA backdoor. That the ME can do networking certainly doesn't give confidence. The US government can order CPUs without ME, but nobody else can. Does not raise confidence either.
On top of that, it is well known that governments research or buy 0-day hardware and software vulnerabilities and keep them secret to be used as weapons.
ME is just a fraction of the attack surface. When I read the title of the article I thought "trustworthy" was about mitigating hardware vulnerabilities.
At this stage it's practically impossible. :(
Trustzone is a secure execution environment, mostly isolated from normal CPU operation. Wasn't it so that it cannot even access main memory???
ME is really more privileged than the CPU?
I have not heard about Trustzone doing networking. But ME can supposedly do even WLAN while the CPU is not running.
Disclaimer: I am not a hands-on expert at that level, more like an armchair pilot...