During a visit to Cisco's​ product security R&D division, I was told that Cisco already has a system in place for customers who want to check for backdoors.

Firstly, they provide customers with all internal documentation on every single device, component, and software. Secondly, if the customer is still sceptical, they invite a team to Cisco HQ. They provide the team with a closed-room environment containing all source code (including HDL) for inspection. The customer can also bring their own devices to test the outputs against that of the reference device they are inspecting.

So, in the case of Cisco, I'm not sure why this is news, since this system has been in place since the Snowden leak.