Despite its unverified fuel savings the operating costs are much like any other plane.
It's expensive to buy and we'll see in 10 years what the maintenance costs are like.
I'm sure I read somewhere, about 6 months ago, that the fuel savings experienced by ANA were actually slightly better than the Boeing claims.
In terms of maintenance, obviously time will tell a better story, but the scheduled maintenance involves a small fraction of the hangar-time of 'traditional' airliners. Very limited corrosion-checking, instrumented bolts and less than 30% of the wiring of a 767, mean a lot less labour.