All indications are that the alignment management for NwN2 is modelled (and improved) on the KotOR2 one.
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But that raises some issues. Would you only be able to multi-class into being a paladin or monk? If you start off at true neutral, you wouldn't be able to yet utilize all class abilities when taking an alignment-restricted core class You'd have to do a LOT of good, lawful deeds before you could utilize the paladin?
What then, eh?
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Just like if you pick a character class that has minimum scores for attributes and that character cannot score lower than that in the generation phase, so too the alignment restrictions would prevent a character choosing to be a Paladin (say) as a neutral character.
I imagine the character generation will be pretty much like NwN.
It is still feasible, too, that the class will also determine the starting alignment, meaning that it is possible to start as true neutral (as a standad fighter, say) or as neutral good (as a Ranger, say).