Also, although the first stage is quite large and has 9 engines, when it finally touches down it uses only the center engine, throttled down. Even using just t

Also, although the first stage is quite large and has 9 engines, when it finally touches down it uses only the center engine, throttled down. Even using just that one engine, it produces too much thrust to hover (grasshopper can hover, but grasshopper is heavier than a returning F9 first stage). The second stage is meant for use in a vacuum so it's expansion nozzle is much larger, so perhaps that extra weight would balance things out a bit, but I suspect that the second stage would have a massive thrust/weight ratio when reentering almost empty. Makes things more challenging, even if the engine does work in atmosphere correctly.