Yeah that would be pretty cool! But I wonder how he would talk to Kakashi, considering they met when he died in Pain invasion, right? Would Sakumo be like, "Oh, so I see you came back to life." or "Huh? I never saw you, it was all in your head." either way, seeing him like that would be pretty cool, but like people have said, he was as strong as the sannin, so maybe having him would kill too many people? I don't think so though, considering several strong shinobi have been beaten far more easily than they should have been....sorry, thinking through typing LOL