Now this seems a highly attractive feature. Has any website used anything like this before?
Not that I'm aware of. Although I'll add it's only suitable for some games. For instance it'd never work in bustabit, because the server needs to know the game outcome (bust) before players are finished making decisions (e.g. they can cashout in real time).
But if I ever got back into gambling (which I have no intention of...) there's no way I'd do it without such a system. The piece of mind knowing wins are legitimate is huge.
Though it is definitely a trust increasing facility it would be almost lost on most gaming scenarios as in any outcome the result cannot be known in advance (dice, roulette, etc)
Nice work though and a great concept to come up with.
I wonder in which scenarios something like that could be best utilised or implemented