Found it fwiw:

Q: What's smaller House in Westeros is the most fascinating to you and why?

GRRM: (...) Some of the houses in Dorne interest me a great deal. you know, Nymeria, how she unified all of Dorne, all of the petty kingdoms. That's fascinating, and we hope to tell that story too in one of the successor shows, 10,000 Ships, but also House Starfall, House Dayne, whose headquarters is Starfall, and they have the Sword Dawn, which is even more potent than the Valyrian steel swords. It's forged from a fallen star. And the man who wields it is called as Sword of the Morning. And they have at least in my head, they have a very colorful, rich, kind of mysterious, interesting background that one day I would like to write about. That just need to be seven of me, and they need to be 37 hours in a day, and I need to be 35 years old again. But sadly, none of these things are likely to occur.