Expect an addendum to the owners manual right after - wear your seatbelt, dont leave children or pets alone in vehicle, dont touch a hot stove or your exhaust manifold bla bla........... "Do not operate vehicle at extreme angles! Runaway may result."
If anyone is really concerned, just install a fire suppression system with a spray nozzle directly into the intake system. The fire suppressant will remove all the oxygen and the "fire" (combustion) will be extinguished. This would be the least expensive/least intrusive way to remotely stop a runaway. Using a throttle valve butterfly would work to lower the RPM maybe to a safe range, but the engine will grab air wherever it can to keep running. Just an FYI, NEVER TRY TO USE YOUR HAND TO ATTEMPT TO BLOCK THE INTAKE OPENING, the vacuum generated could invert your hand, breaking bones.