Well Heim's theory (
http://www.heim-theory.com/ ) is a successful TOE as it predicts the elementary particle masses and the forces using only 4 parameters as input (G, h, Mu and Epsilon) and gives a cosology. So in that sense there is already a successful TOE. But of course, in the wider sense no theory can be complete without consciousness and the ineffable scent of a rose.
Hugh