They're way too common now. Ever since that update where they added the other elite creatures, the frequency of "super edimmu" increased (or at least it feels like it did). I remember it being a bit more rare to get a spawn.
I wonder if they've messed with their blood shard drop rate (apparently 1/50)
.
I don't think the rate has increased at all, at least not personally. I've been getting roughly 5 per task which is in line with the 1/44 (1/47 or 1/50) rate.
Unslain Bosses - Clan