Switching the A340 order to A380s, is probably just the same as cancelling the order. No A380 has yet to be delivered. :)
Cancelling the order? Airbus may as well stop A340 production completely. Why wait 5 or more years to get a four-engined plane that will only be as efficient as the current 777-300ER? I'm sure that by the time an enhanced/high gross weight A340 is certified, Boeing will have improved the performance of its 777's. Why bother getting four-engined planes when ETOPS 240 and 330 will be available?