I have a few thoughts on this, perhaps unrelated to each other.

AUTOMATED_TESTING is not just limited to Perl. It is used by many test frameworks to indicate an automated testing environment -- some know how to read other metadata files, some do not.

Your proposal suggests a method by which the test can communicate to the harness that the test belongs in a certain environment. AUTOMATED_TESTING is a method by which the harness communicates with the test that it is running in a certain environment. Two very different things.

A single test in a test file (rather than the entire set of tests) may need to be skipped if in an AUTOMATED_TESTING environment. Under your proposal, I would need to split this test (along with any initialization, setup, and other concerns) into another file.