I'm confused. Copyleft doesn't grant a right to contribute upstream. It's perfectly reasonable for a maintainer of a copyleft project to say "I only accept contributions if you give me $1,000."
Copyleft grants you the right to make changes and redistribute the resulting work under a compatible license. If you have a problem with CLAs, don't sign them. Many people do not care.
Even without a CLA the author could simply remove contributions and still relicense. This isn't novel, and has been done before.
Obviously it may be difficult to remove contributions.
