I don't think they will bring back characters from the old Krath in TSL. Mainly because most of them died in the war. What I am thinking is the survivors and the descendants of the old Krath have remained in the shadows on Onderon, slowing regaining their former strength and waiting until the time was right to exact their revenge. Revan and Malak's war would have presented the right opportunity to strike since the Republic would be too busy to respond to what seems like a small rebellion on Onderon. Now the reason I bring up Freedon Nadd is because he is the one who passed the ancient Sith teachings on to the Krath. He taught them how to control the Dark side and Sith magic