I've known for a long time about the cut content from Diablo 1. But I thought it was Inarius, not Izual that was going to be in the game. The manual referenced him quite heavily. I believe he will make an appearance in Diablo 3.
I also wonder what the game would've been like had they not cut Tremaine out of the game. I figured he was probably a rank or so lower than Lazarus and managed to escape corruption but had become paranoid and stricken with neurosis after the whole corruption of the Cathedral.