He will never be PM. Labour grassroots supporters may love him but the country at large view him as a looney left nutter.
Never say never. In a sane world, he would never be PM. This is no longer a sane world.
And though he'd be a disaster for Britain, he might be quite good for the Labour party. He'll shake them up, and they certainly need that after a succession of bland leaders led to that general election debacle. And if you think about it, if anyone can get those Scottish seats back, its him.