These are some suggested changes (at least the reasonable ones) that i've seen thrown around:
-Nerf the movement speed of angelic feathers to match body & soul (i.e. bring it down to 60%) & reduce the number of charges to 2.
-Spectral Guise is now a Shadow only ability, with some appropriate talent to replace it.
-Increase the cooldown on Chastise to 45s
The idea is to tone down Holy priests while giving Shadow a much needed boost. Once again, not my ideas, but interesting enough that I thought it deserved discussion.
Edited to add suggestions.
-Put a cap on the movement speed while Spectral Guised.
I didn't mention the Feather or Chastise idea because i've already covered it.