Things get released as GPL or AGPL that were originally BSD or MIT license all the time. The terms of the copyleft license include all the terms of the attribution licenses. Whether this is a valid thing legally I’m not sure but it doesn’t seem anyone’s challenged it. BSD code is often found in closed-source proprietary products as long as the required attributions are met and the original contributors are understood not to be held to any responsibility or warranty.
The licenses tend to say unmodified or modified copies can be redistributed in source or binary form “provided that the following conditions are met”. Relicensing the code in a way that guarantees those conditions are met has been the accepted thing to do in the community for years - whether that’s GPL/LGPL/AGPL or a proprietary license.
The BSD license (which is the one at issue here) does not explicitly permit the licensee to change the license terms of covered software upon redistribution. Perhaps it would be permitted under an expansive interpretation, but under a narrow reading, it might not be. The default rule, however, is that all rights not granted by license remain with the owner.
As you said, the question has never been litigated or settled.