If it auto-fires upon gaining a 6th stack, that would indeed be amazing, but that would be highly unlikely. FoF and BF doesn't work like that; Fulmination sure doesn't. Accidentally getting a 4th Shadow Orb or 5th Soul Shard/Burning Ember doesn't either; why would Icicles suddenly be any different?
Unless you have inside information, please don't act like what you say is fact. Everything everyone else (myself included) has said is pure speculation and opinion.