I wasn't thinking about threesome. Lakrissa in articular is probably the most flirtatious character outside the party in Act 1, and Alfira has long been a fan favourite.
There's no comparison between these two and Halsin/Emperor. If the latter are somehow good enough to romance (??!) then certainly these tieflings deserve consideration.
And who is necessarily talking about sex? Alfira is a musician and Lakrissa a party girl. Their romance could be something suitable. Or maybe even an actual friendship?
I tell you somethings I really don't like is bait and switch and 'watch the npc romance'. The first is flat dishonest and second should be on TV, not rpg. The Lakrissa/Alfira ending was a let down.
I feel like this is not a bad idea itself, adding some kind of friendship with them, as those characters are somewhat unique and when I first met Alfira I was expecting her to play a bigger role. But let's face it: If Larian decides to add another romance, it would be as bad and shallow as Halsin's, so it's better to not have any additonal romances or deep friendships.