I'd love this as well. Having to disband the party before a trust dungeon during the MSQ just feels wonky.

Related: when a quest involves moving into a purple circle to smush some mobs, please make it clearer what will happen if one person in the party kills the mobs while the quest is active for another member in the party. I think at times the quest has progressed for both players, but other times if the second player moves into the purple circle then more mobs spawn... After being burnt a couple times we now always disband the party to make the outcome more intuitive, but really a clear and concise outcome should always happen without needing to disband, both players should feel like they contributed to advancing the quest, and mobs should scale up according to party composition.