That would effectively rely on the doctrine of trade secret rather than copyright. A major difference is that accidental or malicious disclosure of a trade secret usually ends the trade secret status, forever. In an alternate universe where computer source code had never been copyrightable, famous leaks (Microsoft Windows, 2004; id Quake, 1997) would have effectively open-sourced those codebases, and other companies could have openly and legally used them.

As source code becomes more of a generated artifact of software development the way object code is an artifact of compilation, we might be moving toward a world where secrecy, constant forward motion, and moats become even more of an asset (vs plain IP protection).