See also:

Creative Commons has begun a public discussion process for license compatibility evaluation in order to determine whether or not GPLv3 should be added to the list of CC BY-SA 4.0 Compatible Licenses. If GPLv3 is added to this list, then CC BY-SA 4.0 will be deemed one-way compatible with GPLv3, which means that a person can adapt a CC BY-SA 4.0 licensed work and release the adapted version under the terms of GPLv3.

Express your support today, for maximizing freedom through compatibility! :)