I made up an idea and tested it for this reply. It turns out you can use airplane mode for this already!
When you turn them off in airplane mode, they go completely off, and airplane mode remembers their on/off state distinctly from non-airplane mode. You get the cellular disable for free, since obviously if you're disabling wifi/bluetooth radios, you're disabling cellular radios too. (Otherwise what would be the point? Radio paranoia can't afford to be selective if it's truly justified paranoia, and cellular radios are infinitely louder than bluetooth/wifi ones.)
Personally I think this is more “Maybe later” passive aggressive crap from Apple. You know, where they take the option to say no out of the UI.