What's the point of this?
Ignoring that the item itself is meh and that this doesn't help Runepriests at all...it's a bloody rare. That means it's 100% intended to be for DM usage only, to be given to players either randomly or when DMs want it. Why is this not in Dungeon?
...Oh, and the item is terrible. Come on, WotC.
Let's get this straight.
At the start of 4e one of your big brag points is that all classes would be updated and have content as time goes on, too avoid the 3e problems of "only core" classes getting content. So you've failed on that.
Then you change the way items work to create rare items - items that are completely in DM control, the kind of things players shouldn't even know about until it's in their hands. So you've failed on that.
Then you make those rare items their own catagory entirely - finding a rare item is meant to be a really big deal, and should seriously reward the player for getting it. This one strips away your abilities. So you've failed on that.
Jesus, WotC.