I'm still not sure in whose camp Joseph stands, but Edward's group got exiled in one fell swoop? Excellent... the look of despair on Edward's face, that is. And he even literally fell through the floor, downfall indeed. After all that scheming, and then fallen to ruin in one night. With his pals too.
We won't be seeing him again for a while, but I'm sure he still has a role to play. And yeah, since the Mirrors faction that Jeremy was a part of was based in the mines, this one development serves to remove one group from the board, while at the same time threaten another (the Mirrors rebels in the coal mines, assuming I'm not wrong and they're still there). Kate can not afford to fight him at the same time that she's fighting against Anthony, so this is very good timing.
By Anthony's words, it's apparent that Joseph isn't his ally either. Maybe he really is a faction of his own. He is different from the other hedonistic buffoons of the 3rd floor, so I'm hesitant to lump him in with them. Then there's also the growing speculation about whether "Great Grandfather" is actually real or perhaps somebody's soot power puppet...