Flight Safety,
If the USAF wanted 'a smaller tanker' the 767 still isn't the best answer, because it needs such a big balanced field length if it's going to carry anything like its full potential fuel load.
The A330 is better in this respect.
If you were absolutely wedded to a shorter span and smaller footprint (but concrete is cheap) a better solution would be the A310 MRTT with five underfloor ACTs, which boost fuel load to within a gnat's testicle of that of the KC-767, but which do so in a tanker that can operate from smaller air bases, shorter runways, and which ends up with more fuel to give away on the tow line.
Oh yes, and which has a proper wide body cross section, capable of taking standard pallets two abreast, which the 767 can't.
The problem is that Boeing don't have a right-sized aircraft for the role that can stop quickly enough in the event of a rejected take off, and which therefore couldn't use tanker bases like Mildenhall and Brize except after offloading some fuel.