+1 on this.
It would also allow the network to keep stats - whether internally or publicly - on how much content is being generated fresh for Narrative, and how much of it is recycled.
I also think we should consider allowing people who are republishing their own work on Narrative, to provide links to where it was previously published, and check a box as to whether or not they are removing it from the other locations. This would help the Tribunal figure out cases of alleged content theft. If a published piece does not have this data entered, that would be an extra reason for suspicion. If it does have it entered, it provides a starting point for a quick investigation.
The Tribunal could request that the user prove the earlier publications were his, by requesting that they make a small alteration to the published material on the other site, to demonstrate that the account on that site is indeed theirs.
All of this would of course be rarely needed - but probably important that we consider arming ourselves with the data needed to make these checks now and again.
And again, where pieces have been previously published may yield interesting data for the network. Which sites are being considered by our users as being most compatible with Narrative, in terms of what they posted there. How effective are our measures to attract porting of content from a particular platform to Narrative? This data would provide insight into these questions.