'City of Heavenly Fire' Cover in the Works

Placeholder cover art

The last book of The Mortal Instruments, City of Heavenly Fire comes out next year (2014). Cassie informs us that the cover is getting designed right now.

RT @patchcarstairs: " have you got any ideas for a COHF book cover?:)" They're working on it now.
— Cassandra Clare (@cassieclare) May 8, 2013

Who do you think will be on the cover of this last book?