Like in normal warcraft 3 campaigns and multiplayer maps, the hero units differ. In campaign, you've got Thrall, Jaina,Arthas, and all these cool heroes. But in multiplayer, you've got the archmage, farseer, cryptlord, death knight, etc. They're the same unit, but have different appearances. We could do something similar.
As for the naga deathknight. I was planning on a small order of Death Knights and necromancers. We might be able to get both versions of the naga Death Knight (Misha's and mine) in as main or supporting characters. Naturally, if we don't get to play as the other, it'd be nice if they had different abilities. For uniqueness and all that. XD