Any CC-BY-SA import from an external source requires attribution, so we may use this as an opportunity to standardize how we want to attribute externally imported content.
Sounds like a plan.
However, I think we need to keep the obligations absolutely minimal: an author should not have to understand the meaning of dual-licensing in order to be able to import CC-BY-SA-only content.
If possible, that would be great, but I'm not sure it will be. The contributor needs to tell everyone else what license the content is under (that's a requirement of both CC-BY-SA and GFDL, I think, and is also required by common sense), that requires a certain level of understanding.