He wouldn't be good because he can't speak without rambling and repeating himself. Like
@Piemaster said, it could be fine if he could be edited but he'd be a disaster when delivering a live performance in the studio. I don't think that he could operate in a presentation team and he'd not fit with the remainder of the Top Gear crew.
I'm not over enamoured with Clarkson but I don't think that Top Gear would be as entertaining without him and perhaps it's best left dead should Clarkson and the BBC go their separate ways.