That's what I plan to do if I ever get my project off the ground. Based on the research I've done it seems as though the GPL is fine to use for related data and assets, but I feel that CC offers similar protections for assets and is generally easier to understand.
One thing to note is that if you wish for your game assets to be licensed under CC BY-NC-SA (Non-Commercial ShareAlike) it should be kept separate from your GPL'd engine. The GPL allows code to be used commercially and is incompatible with licenses that explicitly disallow this. If your assets are CC BY-SA (version 4 or higher) I think it'll be okay to keep everything together.
Note that I am not a lawyer, and my knowledge of licenses comes from research and sifting through a lot of very boring reading material.