If the MRTT is an off-the-shelf solution to a fairly generic and previously solved need, why choose a more complicated and expensive design that continues to struggle to get off the shelf? The KC-46 promises to solve a variety of needs, one of which (the primary?) is tanker. Someday, years after it was promised, it may be a fully, no-holds-barred, operational tanker. If we get half the lifetime and utility out of the KC-46 that we did from the KC-135, it will be a miracle.