As for your idea of poly lemme say this. It's not worth the effort, it will never be good, I think Pathfinder Kingmaker was the closest I ever played that had this option explored, but in both options, the sisters and Octavia and her partner, was disappointing in the end. I'd prefer if they don't try to mess with this, I mean, my guess is that Lae'zel will have an open relationship (willing or not for the player), she doesn't see the player as her partner but just a toy that belongs to her, and she may want to have more than one.
Fair points, but also "it won't be good so why bother" is among the reasons that a lot of things were resisted in the past, so hopefully someone will make effort to find what works eventually.
