Cost would only change by a nickle. A simple mosfet would handle it. As a manufacturer I would put in place a set voltage that when the transmitter was turned on if the voltage did not exceed (say 8 volts) the rf transmitter would never power up. Therefore it would not only prevent a flight with a low pack from starting but would also allow the disconnection of the pack once it dropped below the 7.2v. This gives one plenty of time to land if in mid flight. Low battery beeps are great but I can't hear them in my basement.
I suspect there is a defined voltage that once dropped below the rf transmitter becomes ineffective anyway. And if one wanted to get picky have the option in the computer display and set it to default to off so that covers the manufacturer but also allows us to turn the battery protection on.
"While nobody should"...
Exactly. Why doesn't the manufacture prevent this? Gun manufactures put a safety on a gun so that the owner doesn't shoot themself accidentally. Same concept.
Just thoughts.