I've worked (as an IT/desktop support person) with some of our animation artists, and I found ProRender was a very promising project which immediately failed for us with no real hope of recovery.
The issue that we had was that a lot of functionality that works in Cycles didn't work in ProRender, which would have required our artists to rework potentially large parts of their 3D scenes, and to also use different techniques to accomplish certain affects in the future (meaning many tutorials or examples might no longer match up).
I'm not sure what the specifics are, since I didn't really understand how 3D scenes are made, but basically something like some texture effects or something (??) weren't available in ProRender, and so those effects would have to be removed or redone. Unless they've changed something since then (added support for whatever it is), I think this will still be the same issue.
The issue that we had was that a lot of functionality that works in Cycles didn't work in ProRender, which would have required our artists to rework potentially large parts of their 3D scenes, and to also use different techniques to accomplish certain affects in the future (meaning many tutorials or examples might no longer match up).
I'm not sure what the specifics are, since I didn't really understand how 3D scenes are made, but basically something like some texture effects or something (??) weren't available in ProRender, and so those effects would have to be removed or redone. Unless they've changed something since then (added support for whatever it is), I think this will still be the same issue.