Whatever role he's being eyed for, it's the lead one. And it is a good choice. Depp is one of the best actors out there. His work is not all zany Tim Burton romps (and I'd be a little hard pressed to describe what he did in Sweeny Todd as zany anyway). He could easily pull off just about any of the playable races in voicework, though if it's live action, gnomes are probably out.
So far they seem to be making decent choices. I like the director too. Many more pieces need to come together before I start thinking the movie can meet the expectations it's built up, though.