Why that drastic, checking system state (telemetry) can be done using 'data diode' style networking - one network just broadcasting sensor data, other network allows changing parameters and 3rd one allows allows software upgrades and so on.

You can be very defensive and design any remote sensing controller to act as two systems - one management cpu only does data routing (no other connection than administrative tasks), sensor cpu works only with sensors. As bonus you can have management cpu act as active firewall.

Main problem it is necessary to have in house expertise (hw, fw and process knowing) which in making company lean are optimized first and outsourcing custom solutions suddenly too expensive.

Or you can just slap a lot of Windows XP boxes with closed source control software and remote access software and let the central team do it. Which will be a bit cheaper