This has been a popular request throughout early access, so I wouldn't be expecting it to come in an imminent patch if at all. Particularly as it doesn't seem a simple thing to add given the way Larian have implemented conversations (well, some possible "solutions" might be simple, but I suspect would introduce different problems and dissatisfactions).
Which isn't to say we shouldn't keep asking. You never know, if people keep clamouring for a way to get parties more involved in dialogues, or the ability to swap characters in dialogue, then eventually Larian might prioritise it. It was amongst my top five hoped for features in the game, though I never held out a huge amount of hope.
I can't find one of the other threads I know we've had on the topic right now, but if anyone else has a link please do share!
