Alas, I do not have access to the blizzard US forums (damn them for making EU users lesser users anyway), so maybe one of the US posters here could be so kind as to post something about this issue on the US forums? I'd really love to see a blue reply to this question.
Divine Hymn is a pretty lackluster spell, I think we can agree on that. But at least it would be a second CC in PVP. But it cannot even be that, because when you use it you get 30 seconds cooldown on psychic scream, and vice versa. I so fucking hate that from the second I realized it. There is not a single situation where DH would be better than PS. If you could DH when PS was on cooldown though, it would find its (little) uses.
The last thing I read from blues about the Priest Hymn issues was "we have something planned for them, but its not a priority". Meh.
So could someone try to post on the US forums about the shared CD issue? I think if the shared CD would be removed the spell would go from absolutely useless to sometimes very useful. Which would be like a 1000% boost.