There is a New Standard A330 'green' aircraft for new customers' MRTTs; it is not based on the A330neo.
But with the emergence of the A350XWB, it is likely that redundant A330 airliners could be converted into a 'lite' MRTT configuration for 'price sensitive' customers, as was the case with the A310.
Several years ago, Boeing themselves admitted that it would not be possible to develop the 787 into a tanker as it didn't have the 'necessary configuration', whatever that was supposed to mean.
So the future still looks like A330MRTT or KC-46A only - although the KC-390 might have some limited potential, much the same as the KC-130.