It does help with prior versions, since you can use CC BY-SA 3.0 material under CC BY-SA 4.0, which is GPLv3-compatible. (See https://meta.stackexchange.com/a/337742/308065.) It doesn't necessarily help with future versions.
I stand corrected, thank you! I forgot that CC-by-sa included an automatic upgrade clause, unlike many other licenses that require an explicit "or any later version" to do that.
