- the connector is a power connector not a data-connector !
- as it is described as a "spare" Cisco may use this pin on future power supplies without any notice
-> troubles when the power supply needs to be replaced.
- if you want to use this pin you need to open the box to connect some signal inside the box to the pin
=> NO in my opinion this not available as a GPIO pin.
- if you DO open the box you can also add an extra connector or cable leading outside the box
