I do agree with UltimaLimit. I some games the elements just aren't good enough. If we look back to FFI, we there have four fiends, each defending a element, plus we have a Ice Cavern, That makes:
Earth
Fire
Water
Wind
Ice.
I think these five should be standard is the games. These are the five bassical elements of the world. Ice is even a form of water, so. But these five should be always available in a FF-game. Then about other "elements" like Holy and Shadow. I don't really consider them as a element. They are both two opposite. They are like the ultimate black magic (Shadow) and the ultimate white magic (Holy). They should always keep it till last and even then it must cost a lot of MP and gil. If you receive these spells in the beginning of the game, it will lose all of it's "magic". So the spell system must be looking something like this:

Earth, Earth2, Earth3 and Earth4 (the same for Fire, Water, Wind and Ice)
Holy
Shadow (or a different name)

I think this looks actually very good. Throw in some healing spells and some status spells and your finished.