@Eli: I believe the auto-create was removed with the earlier redesign but crept back in later so I didn't view this particular jira as incompatible. Since the goal has been to mimic the real shell, this non-posix "feature" was intentionally (again?) removed to solve this jira.
It also resolves the inconsistency between single source vs. multiple sources copies. Single source copy would formerly auto-create non-existent dirs, but a multi-source copy fails if the target isn't an existing dir. Ergo, copying a glob to a non-existent path was indeterminate depending on the number of glob matches: 1 match auto-created, more than 1 match failed.
Internally, we found the impact to be minimal (a single mkdir), so we favored retaining the posix semantics of copy. Some relied on the auto-create because mkdir failed if the directory already exists, thus
HADOOP-8175 added a -p flag.
If you feel strongly on restoring the former non-posix behavior and single/multi source inconsistency, I can look into doing so.