21. In order to get unique dialogue for each character, you have to have that character selected, then go talk to whatever NPC would give unique dialogue. Unique dialogue interractions should be automatic so you don't have to search for them and potentially never find them. How could I know that the random dwarf in the town's square has unique dialogue for Lohse? Unless I check him, and every other NPC, one by one, with all the party members, I'd never know there is a cool bit of dialogue hidden in there. Why not have NPCs with unique dialogue address the party PCs directly, you know, as if they recognize them or something?
I think it would be hard to implement that while retaining multiplayer independence. I'd say that is what multiple playthroughs are for in singleplayer.