We would use this for when a mod moves on to another job. It's nice to be able to change the author to someone actually still working with us.
Kinda hope this is already in the works though, since the update for drafts. :)
I agree. The typical usecase was already mentioned by @Paul_, that when the original author leaves the job and another team member takes on the task of updating content, then the author role should also move to the team member.
Hi @Scott Baldwin! It is our intention to follow up the release of the “create on behalf” feature with its sister feature that would allow the author to be changed on published articles and product updates, so thank you for submitting this idea.
Updated idea statusNew→Open
Updated idea statusOpen→Added to Backlog
Really interested to have this feature. Upvoted. Thanks!
Updated idea statusAdded to Backlog→Under Construction
Updated idea statusUnder Construction→Delivered
Thank you all again for contributing and collaborating with us on this idea! We’re happy to announce its release
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And for more details of the functionality please visit the How-to guide in our Knowledge base:
I didn't think much of this feature until today when I actually had to ghost-write for Track-leaders for our conference we are prepping. v handy idea indeed @Scott Baldwin and thanks @Cristina and team for delivering. 
Btw, are the newly assigned Authors notified when I make this change, I’m imagining, like when we assign Moderators for threads?
And oh, we are attempting creative stuff with Community-powered event at Gainsight
Happy to share with anyone interested. :)
They are not notified of the change.