While I would love a feature that shut everything down (more thoroughly than just auto shutdown short key does, or the way the plane gets loaded in shutdown state), there's practical problems with that wish:
many FSX planes have fuel valve, mixture, battery & generator switches... but lack these features in virtual cockpit.
If you put them to cold and dark position, you might not be able to start them without resorting to CTRL+E cheat (or whatever was the default hotkey). Example: jet planes that refuse to start with "mixture cut-off" even though that mixture lever doesn't even exist in VC (engines only have on/off valves and throttle). You just have to guess what the problem is and add more mixture via keyboard or joystick hotkey moving an invisible mixture lever that doesn't exist in your VC.
There's just too many inconveniences that arise from forcing a cold and dark to a plane with incomplete VC, most of which prevent you from starting engines manually. Even just using auto shutdown to force a semi-"cold and dark" condition may produce an un-startable airplane already. True cold and dark with battery, generator, mixture, fuel valves, mags, avionics... everything turned off. Sounds bad to 99% of FSX craft. And what's the point in having a cold and dark cockpit if you aren't going to do the start-up by the book (=manually)?
It sounds like one of those "too good to be true" things, unfortunately.