cc-by-sa became gplv3 compatible. Cool! I forgot that.
Still not gfdl compatible. https://creativecommons.org/2015/10/08/cc-by-sa-4-0-now-one-way-compatible-with-gplv3/ In that light, I hope it would be allowed. I fear it's still an exception that rms would have to approve :(. As far as I can recall, we are not allowed to accept gpl for manuals, although that seems draconian and I can't find any explicit statement about it right now :(. Hmm. I hope I'm forgetting something. -k