God mode is basically a form that leaks out zero Ki which changes the quality of it. Think it went along the lines of that anyway. And you can attain it simply by training in the right way. I don't think Krillin will do that because he seems happy. I just want Gohan to achieve that form. Maybe even throw in something crazy like since he is a half breed he gains the quality of two god ki or something like that. Make him relevant again. Hell...I'll even settle for Piccolo getting a God form.