While this option is not implemented in RutOS, it might be possible to achieve it using a custom Modbus register.
This would involve reading and parsing the WiFi STA interface SINR and/or RSSI parameters by using the command wpa_cli signal_poll.
Then this data could be stored in a custom Modbus register and read using a Modbus TCP Master.
Then a Modbus alarm could be created, and as an action, Modbus Write Request should be chosen. The values that should be written can be found here. In particular, registers 391 and 392 should be used to toggle 2.4GHz and 5GHz WiFi.
One downside to this approach will be that the WiFi will need to be turned on manually. Of course, another script could probably be written to create a work around, but it seems like this could cause more issues than it's worth.