Good intention but don't think a standard merc switch would work, maybe a modified one that wouldn't give false trips.
You might be on to something though, we've got safety switches for everything else. if you could come up with a cut out mechanism to prevent roll over you'd be a hero, save lives and make a bunch of money. Especially if it was simple enough to retrofit older equipment.
Ironically one of those flippin little safety devices almost cost me my life, took my little outboard motor boat for a cruise on the CT river, as soon as I got out in the current the motor cut out and I couldn't get it to restart. the swift current was pulling me at it's will right for a bridge abutment. luckily another boater spotted me in trouble and towed me to safety. Turned out to be bad merc switch, designed to prevent motor from running/starting when tipped up.