remains to be added: FSF suggests to add components for no other purpose than blocking a feature like updating the modem firmware. It makes sense for FSF to ask for tweaking the design into something that fits into their political agenda around RYF (peripheral == "a blackbox that doesn't have visible firmware"), however for the user this definitely doesn't add to the value of the device. And in the end of the day it's not feasible since such a blocker circuit inevitably consists of a MCU which again has firmware, and we don't want to add our own BLOB firmware in MCU on top of the modem firmware BLOB. But then when MCU is no BLOB, user can modify it and thus re-enable the modem update feature.
And actually you never can provide proof that there's no hidden path to still update the firmware blob in your peripheral, no matter which measures you implement to block such feature.
Same general plot appies to other peripherals with BLOB firmware, like WLAN.

excellent idea
/j