User blog comment:B214/Volume 23 discussion blog/@comment-31137559-20170508172118

Gremory(Duke), Sitri(Prince), Phenex(Marquis), Bael(Great King), Agares(Archduke), Glasya-Labolas(Count), Astaroth(Duke), Belial(King), Furcas(Knight), Balam(King), Amon(Marquis), Vassago(Prince), Gamigin(Marquis), Forneus(Marquis), Barbatos(Duke), Vapula(Duke), Vepar(Duke), Crocell(Duke), Bune(Duke), Andrealphus(Marquis), and Sabnock(Marquis).

So far those are the houses and former houses of the 72 Pillars that have had members introduced so far. I wonder which is the next house that'll be introduced.