Obviously I'm biased, but the Banefort-Ironborn dynamic would be so damn interesting to explore? The Baneforts being the northernmost house of the westerlands, incredibly isolated from other Lannister bannerman (by a literal mountain range), versus the "independent, fierce, and sometimes cruel" Ironborn, who typically have "no love" for the mainland Westerosi. Would they have a weird sense of kinship, or would there be a bitter rivalry between the two?
I like to imagine the former, as I don't think the Baneforts could survive with relentless seiging by the Ironborn - it would make sense if the house would makeup a significant amount of their limited trade with the mainland. Plus, it's pretty clear that the Baneforts are also a house of the First Men like the Ironborn, which is pretty unique for a group south of the neck.
Just going off from there, the Baneforts are in such a massively unique position, at the intersection of so many regions of Westeros - northmost of the Westerlands, closest house to the Iron Islands, near the border with the Riverlands, and sharing the Ironman's Bay with both the North and the Riverlands.
I've developed this idea of the Baneforts being the weird goth edgy bannermen of the Westerlands, with their connections to the Ironborn and other more northern houses, as well as by virtue of their First Men heritage and being descended from the Hooded Man from the Age of Heroes.
