My favorite theory so far is still that Halsin is someone's OC. If I looked at him through the scope of a smut fic his personality makes more sense to me. Funny theories aside, I do think they need to correct the way poly is handled. Good faith or not it's kind of a mess in my opinion.

The only 'real poly' options are a Halsin trio.

Despite setting up a system for monogamous/poly characters, monogamous characters still do not react or care if you sleep with
The Emperor or Harleep.

The two characters they chose out of everyone for a Halsin trio are the two I would never introduce to poly. Shadowheart literally does not have her memories for most of the game (and seems to be very committed to the PC in her romance path). Astarion was a sex slave who's afraid to lose the only person who he cares for. I honestly think Gale having a fuck it,
I'm dying
moment (also he can be persuaded to join in with the twins with a persuasion roll so it doesn't seem that far off for him) or happy-go-lucky and touch-starved Karlach being open makes more sense to me.