I would love to see Kang, Kor, Koloth, Kruge or Chang in Star Trek XIII. However I feel STID again reduced Klingons to beat'em up fodder. Klingons always seem to be the whipping boys for heroes and villains.
That said I wouldn't mind seeing either:
Arik Soong's descendants and an army or androids.
An updated version of the Doomsday Machine. A giant space cone is a little dated.
Or an original villain like Nero was.