kitbashing is always allowed, kitbashing bad is wrong.
look at the RN AU: all of those are in effect modified variants of never build and real designs.
in the archive (you should check the forum and peoples worklist yourself) we miss the ships from DD-662 to DD-962. we also miss DDG-31 to DDG-47. I would suppose there would be some classes in between
if there would still be no light, I would like to point at the DE's and the DLG's, were some classes seem to be missing as well
now, never again say there are few undrawn ship classes, let alone the variations
EDIT: ow and, we are still recruiting people for work on the USN carriers, as the drawings we had were so wrong they were removed from the main site....... but the people who would do them (including myself) lack the time, knowledge, interest or some other factor that would make huge projects like carriers impossible to do alone.........