They talked about no multiclassing and why on their forums:
https://www.realms-beyond.com/forum/index.php?topic=109
We will have prestige classes but not multi-classing. You can create your party with up to 6 members (covering 6 different classes) and multi-classing would be just too much extra development effort to implement.
But many of the prestige classes require you to multiclass first
I'm going off of my memory of NWN 1 & 2 (which I know changed some stuff from 3.5 PnP), but I don't think many of the prestige classes Hobs mentioned as potential actually require multi-classing to meet the prerequisites (though it might be a good idea for some)... Eldritch Knight comes close (need 3rd level arcane spell & "Martial Weapons Proficiencies"), though from the wiki I gather NWN2 changed is slightly so a wizard / bard could just take martial weapon proficiencies as one feat if they don't want to take a level in a fighter class.
At least pre-reqs for Arcane Archer, Arcane, Blackguard, Dragon Disciple, Duelist, Dwarven Defender, and Shadowdancer can all be achieved with a single class. Would have to look up the others that Hobs mentioned as they aren't in NWN.. (Ok Arcane Trickster requires Sneak attack & Arcane Spells so that is one that would need MC). Of course, it's also possible Ceres could just change the prereqs for any of the prestige classes as they're changing wizards to be more like sorcerers.
However, I am pretty much at a loss as to why implemented multi-classing would significantly add to the development time. Wouldn't the only new things that really need to be implemented be "favored classes" for non-human races and the XP penalty if your characters who aren't Humans or Half-elves multi-class outside of those parameters... So unless I'm forgetting something, this doesn't seem like something that should be hard to implement...
Without bards and multclasses, I hope it will have some good magic warrior-like prestige classes
The prestige classes said to under consideration as of December are:
Arcane Archer, Arcane Trickster, Archmage, Assassin, Blackguard, Cerebremancer, Dragon Disciple, Duelist, Dwarven Defender, Eldritch Knight, Elocater, Hierophant, Horizon Walker, Loremaster, Metamind, Mystic Theurge, Psion Uncarnate, Psionic Fist, Pyrokineticist, Shadowdancer, Slayer, Thaumaturgist, Thrallherd, War Mind.
So yeah ,you'd have options for magic warrior builds.