Interestingly, this suggests we can't practically incorporate BY-SA material first published elsewhere into Wikinews without the consent of the author(s)...
That would be the case anyway, I think. Wikinews is CC-BY, not CC-BY-SA. you can't re-use SA material into a document that is expressly licensed as not requiring SA. you would need per-document additions to the license, which are not practical.
--Andrew Whitworth