[webmaven]

> I think in these cases to receive contributions you must ask people to sign a CLA that transfers the copyright to the you/project. Otherwise it's not possible to relicense the contributed parts.

This is a common misunderstanding. A CLA allows relicensing of a contribution, but doesn't require transferring of copyright.

Transferring copyright is only needed if you want to allow changing the terms of licensing unilaterally in the future (for example, you contribute under GPL/proprietary terms today, but the company decides to change the license of your contribution to proprietary-only in the future), and makes suing for license violations a bit simpler (since one entity obviously holds the entire copyright). Technically a copyright assignment could even allow the assignee to sue the assigner for a licensing violation.

In other words, copyright assignment really isn't needed for anything reasonable a company might want to do. Only for things (like reselling the copyright to some other company or making the code proprietary only), that you wouldn't agree to if it was spelled out in a CLA.