I imagine that the two characters will have individual skill paths. There would be some cross over (eg. Weapon Expertise), but I reckon that one will have "good" spells and the other "evil" spells. Also, you'll be able to play as an evil character now. You'll probably have to do some balancing with the good/evil-doing so that both characters can rise through the levels.
I really don't know how it's going to work, this is just how I envision it.
