Part of the trouble with this is that we don't really know what kind of demonstrations would be within the power of a superintelligent AI. If the coin comes up tails, do you get to say "I've got a rigorous proof of my friendliness which I can show you" on the presumption that you can mindhack the reader into thinking they've seen a rigorous proof? Do you get to say it if the coin came up tails on the presumption that a superintelligent AI could come up with a proof that a human could actually verify? Declare it off bounds because you can't come up with such a proof and don't think a human would be able to check one that an AI came up with anyway?