If the contribution is into an open source project on, e.g. github, the contribution is already covered by an open source license the contributor is aware of. I

If the contribution is into an open source project on, e.g. github, the contribution is already covered by an open source license the contributor is aware of. If the copyright owner takes it private, they cannot revoke the existing GPL license on the existing code base - only changes from that point forward. At that point, the contributor could take the existing codebase and fork it to keep it open source. Of course, they can only do that under the existing license so they have no power to change the license themselves. What CLAs do allow (that IMHO is beneficial) is the copyright owner developing other licensing options for specific customers. This can provide a better income source than just “support” for a project.