He would have been mad to "rule it out". He knows how MPs work and wouldn't put it past them to continue trying to block it. While I have always liked Boris (i know...) i also think he has enough charisma, ego and arrogance to not want to fail at what he has said. He seemed to deliberately step back when May came in to allow her to make the mess and be the scapegoat, and was always likely to turn up at the last minute and get on with it. But that is what we need right now.