Supposedly at James' Q&A at The Harvest, when asked about his role on Angel, he said something along the lines of 'I will have a soul and I will be a....' at which point the crowd shushed him.
I'm guessing he was going to say he would still be a vampire. Whether Joss originally toyed with the idea of Spike shanshuing, I think there has been too much presumption that that is what would happen. Therefore, it ain't going to happen.
I originally questioned having two vamps with souls on the same show, but now I think it may be quite entertaining. DB could finally get to show his humorous side playing Angel's jealousy (we already saw a hint of it in Chosen) and perhaps his resentment that Spike seems to be dealing with it better (in my opinion).
Then again, maybe James was going to say "human". Or, more likely, he doesn't know what the Hell he's talking about. :p