As a total layman when it comes to air gapping: Would this not be defeated by putting the computer in a faraday cage?
If you want the thing you're isolating to be useful to you at all, you will need to have some physical connection between the inside and the outside, i. e. a hole in your air gap.
With a suitably tightly focused telescope you could pick up the LED blinking and decode the data going over the port.
Of course, now you've got a Tesla coil in your data centre, which will bring you a whole new set of Interesting Problems to cope with.