Have they addressed how they're going to address the specific class abilities with multiclassing? I assume I'm not going to be able to, for example, take a rogue and add a level of paladin just to get the defense buffs from alignment. Do you just get a little bit with each level of the class?

Yes they have, its covered by power sources.

https://www.pcgamesn.com/pillars-of-eternity-2-deadfire/pillars-of-eternity-2-multiclassing

Huh, interesting. Thanks!