Basically, this methodology would enable attackers to siphon passwords or security keys from a protected system, before transmitting the data to an internet-connected system which remains in close proximity that is obviously controlled by the attackers. Apart from that, the internet-connected system can be used to send malicious commands to the air-gapped system with the similar technique, now how about that?
Of course, both systems will need to compromised with malware before that can work, and the attack will cater for a mere 8 bits of data to be transmitted over an hour in a readable manner, which is alright for a password or secret key, but definitely not being able to handle copious amounts of data.