I totally agree to keep it simple except for that extra opto kill switch. A power expander is located before the receiver(s) and if it fails, everything else fails. Same for redundant battery systems. Your engine's ignition is powered independently though.

Only at the field I'm currently flying at for 6 months or so I have seen a few gassers and jets gone wild. A friend of mine w/ his 35% Edge for example. He used a redundant voltage regulator and 2 LiPo batteries but it wasn't so redundant. It drained one battery, lost power to the Rx and servos but the engine kept running. He was lucky the plane crashed in a lake a mile away not far from a populated area.

Some day we all experience an electrical failure if you like it or not and once that happens, it's good to know your plane can't fly into a crowd w/ the throttle wide open.