Juliet L. Hardesty and Nicholas Homenda have published "The Ecosystem of Repository Migration" in Publications.
Here's an excerpt:
Indiana University was an early adopter of the Fedora repository, developing it as a home for heterogeneous digital library content from a variety of collections with unique content models. After joining the Hydra Project, now known as Samvera, in 2012, development progressed on a variety of applications that formed the foundation for digital library services using the Fedora 4 repository. These experiences have shaped migration planning to move from Fedora 3 to Fedora 4 for this large and inclusive set of digital content. Moving to Fedora 4 is not just a repository change; it is an ecosystem shift. End user interfaces for access, management systems for collection managers, and data structures are all impacted. This article shares what Indiana University has learned about migrating to Fedora 4 to help others work through their own migration considerations. This article is also meant to inspire the Fedora repository development community to offer ways to further ease migration work, sustaining Fedora users moving forward, and inviting new Fedora users to try the software and become involved in the community.