When shadow spec is well.. shadow, and not- unholy?
A priest saying that he specialises in light/shadow magic sounds more fitting than saying that he specialises in... holy.
Seems inconsistent ;]
Current naming seems outdated since whole "light" is no longer based on christian religion but rather chinese philosophy, namely "yin yang"
for paladins "holy" still fits tho, as they are by default "holy warriors" but priests understand/control/use the other side too.
What is void to a shadow (and vice versa)?