The ability to have Plex Media Server directly pull from a distributed backend such as Ceph Object Store would be wonderful. There is a point where you have to start distributing a media library between systems (assuming keeping costs at a minimum). Native Ceph support would allow Plex to take advantage of Ceph's distributed, redundant nature without a lot of work. While doing something like this is doable via Ceph+Lustre or Ceph+<file system of choice>, it's a lot of extra overhead and makes it harder to run multiple Plex Media Servers.
Based on my experience with Ceph and such I'd think using one Ceph object per media item would work. That would let Ceph keep the object distribution balanced and replicated (if desired) without having anything get to big. I'm betting that the Ceph API could be bolted on right at the file read/write layer of Plex Media Server.
tl;dr Add support for media stored in objects stored in the Ceph Object Store.
Ceph home page: http://ceph.com/