Apparently Jetstar have been overnighting A330 crews in DPS for up to 5 days at a time virtually on standby in case the 787 goes tech. I guess if an 330 needs to come to the rescue, there will be a crew in DPS to fly it back home again.
Not saying it's a correct decision but the cost of this would certainly be much less than that caused by a delay arising from a type change, not to mention the aggro from the travelling bogans.