I think I noticed something. When
Prismatic Omen is in play, 'buffs' like
Armored Ascension and
Blanchwood Armor seem to work. IE: They see all your lands as plains or forests or whatever. Same goes for mountains too, for example Valakut gets triggered once you play a bunch of forests or plains or whatever else, because they are considered mountains thanks to the
Prismatic Omen. But if you use magical hack and change the blanchwood armor to use swamps, then it does not see the lands as swamps.
So maybe
Cabal Coffers is ok, and maybe it is just that the
Prismatic Omen turns the cards in to everything except swamps?