ACPI, firmware, and your security

On his Google+ page, Shuttleworth says

  There's a big debate on at the moment about whether to
  adopt historical, insecure-by-design 'standards' into the
  next generation of cloud server systems. ACPI, and the whole
  PC firmware blob mess, are attack vectors that we cannot ever
  fix. We should not design them into the systems that we and
  others will depend on being trustworthy.

So it looks like this is about servers, and not (necessarily?) phones.

(edit: formatting)

Context: HW vendors push to get ACPI on ARM servers, https://lwn.net/Articles/574439/

Well, on x86 there is already SMM and it predates ACPI by years. I believe that ARM SBSA is targeted at only servers, where even HP don't restrict access to firmware updates that solve security bugs.