This is not correct. The copyright owner can, by definition, do whatever they want with the next version, as long as they hold the copyright for the entire code

This is not correct. The copyright owner can, by definition, do whatever they want with the next version, as long as they hold the copyright for the entire code base. Nothing ever prevented MySQL AB (or Sun) from shutting down their public repos and releasing the next version of MySQL as proprietary software. Of course, this would almost certainly lead to an immediate fork, but it has always been possible.