Claremont's Hellfire Club was an interesting addition to the X-Mythos. After him, it fell in significance to the point of becoming a parody. While he ultimately wasted it in his Hellfire and Brimstone arc, I did enjoy Millar's more direct correlation to real world secret societies(Freemasonry, Illuminati, etc).
Given Emma's reapplication since Morrison as an X-Man, even if she has apparently gone 'bad again', I doubt modern Marvel will lean into the more obvious occult aspects of the concept in lieu of just 'rich people being naughty', as it is often positioned as, but in theory the Hellfire Club could be a very potent, and scary, antagonist for the X-Men.
I would love to see a re-imagined Inner Circle of Amahl Farouk, Selene, and straight up evil Sebastian Shaw and Emma Frost just go hard with the debauchery and evil magick and all that, trying to enslave the world under their iron fist, but such a story is probably too much for Disney-Marvel at this point.