It's seem everyone forgot about Kankuro. Shino, Kiba, Neji already made a come back in event, next gnw ninja will be Kankuro or at least he will make a comeback in event too.
For signin daily I think it will be Sai then they will update the game to add more gnw ninja : gnw ino, gnw sakura, gnw tenmari, etc... and begin a new cycle of signin rewards while eventually add old gnw ninjas into exchange shops.
That is just my guess but at least it make sense. Hopefully.