A concession speech would require him to recognize that he failed, and I think his ego is too big to allow for that. He will claim "crooked Hillary" rigged the election until the day he dies, all the while blaming everyone but himself for the loss. Such is the contradiction that is Donald Trump.
Even if the open windows of science at first make us shiver after the cozy indoor warmth of traditional humanizing myths, in the end the fresh air brings vigor, and the great spaces have a splendor of their own - Bertrand Russell