(And the vulnerability you mention doesn't seem to apply to all 'wifi anything.')
What I am saying is the types of security used on 99% of residential WIFI networks is about as secure as a screen door, WEP (Wired Equivalent Privacy), WPA (Wi-Fi Protected Access) and version 2 of the WPA2, this is the encryption the WIFI radio devices use to send and receive all your private data.
From an attackers perspective they need to intercept this radio signal going between a client and a WIFI router, and from a far distance.
Picking up data from a WIFI printer in your home office from a far away distance is difficult because of walls, proximity of the WIFI printer to the router, etc.
If a PV device on a rooftop such as a optimizer needs to transmit a WIFI signal to a residential router then the router transmits it to the inverter, that is a likely vector.
Once in the network, the firmware of the roof top device is updated with new firmware from the attacker and now functions normally to the user, but now provides a ongoing port of entry, that is one example of many.
If the PV devices are hard wired with cheap cat5e ethernet cable there is no chance a WIFI security hole is created, zero.
Don't trust me, do your own research, consult an IT security professional you trust to review the equipment your installing in peoples homes, every one of these WIFI things are like adding a screen door in someones house.
Same thing with WIFI cameras, WIFI thermostats, dimmers etc.
The thing about PV is the CPU horsepower is way better than a camera and the rooftop location is an ideal radio antenna.
EOT