This is pretty cool. About the only brigade that has 2 curses which almost any deck could benefit from having both active at the same time is crimson (Captured Ark & Go Into Captivity). Of course specific decks would also benefit (ie. Unknown Nation & Given over to Egypt in Egyptian decks).
My main problem is that the limitation still wouldn't stop you from still having 2 different brigade curses in play. You could have one in the fortress and another on your regular art pile. There are already starting to be a LOT of defensive arts in play these days with Magic Charms on a magician, one in a temple, one on the art pile, and occasionally another one in a fortress (ie. UW on HPP).
Of course maybe this would get more people to actually put Split Altar in their decks. Nah, probably not
