"The fix is the -T (--no-target-directory) option, which tells mv to treat the last argument as a plain name instead of a destination folder:"

No the fix is to mark the move-into-folder behaviour as a bug when --exchange was given.

Why? --exchange already tells mv to expect swapping 2 files (or directories). Read: taking that as "move into directory supplied by 2nd argument" violates users' expectation, violates the principle of least surprise. And THUS should be considered a bug.