Doug Jones, probably a creature of some kind. Perhaps even Thranduil?

Anywho, I think at least some of the concept art we've already seen predated GdT's departure, but agreed that hopefully we'll get a more concrete idea of what his TH would have been like (perhaps on the EE release)?

Here's a comment from GdT concerning stuff he showed to James Cameron, I believe back in 2009:

"...very strong designs and maquettes: GOBLINS and their environment, SMAUG (fully designed but without final color / texture), SPIDERS OF MIRKWOOD, MIRKWOOD, STONE TROLLS, WARGS, IRON HILL DWARVES, GUNDABAD ARMY, THRANDUILL’S THRONE ROOM etc, etc"

Though I doubt they will I hope some storyboards or even scripts for earlier versions of TH surface at some point.