I would love to be in a tarot-based RP.

Cliques/rivals or common foe... or both, even.

I second [@The Hobb]'s idea of having factions for each of the four suits. They could either be more like their own kingdoms or sectors of a single government. In the case of suits as individual kingdoms, the Major Arcana would likely be saints/heros who are not bound by the kingdoms. In the case of suits as parts of one government, the Major Arcana could also be royalty or special appointments as well as saint/hero.

In addition to the Major Arcanas being PCs, I believe the King, Queen, Knight, and Jack of the suits all have potentials of being interesting PCs as well. But, of course, it'll also depend on the setting.