I'm just a layman, so this post might be extremely naïve and short-minded of me, but I'll go ahead and post it anyways.
As far as I can understand, the main problem we have with the GFDL is that you have to include the entire text of the license if you want to use something that is GFDL. Why not, in the next GFDL version, just remove the clause that says you have to include the entire license, and just say it's sufficient to state that the material is GFDL and credit the author(s) in the appropriate manner? Wouldn't that - for the everyday person - accomplish exactly the same as switching to CC-by-SA?