Geo already works in an MMO, XI. Not saying it has to work the same way, but it work.

The biggest flaw about having it in this game is I predict it would most likely be a DPS Mage with spells like Eartquake.

Btw, no, a RDM is not a jack of all trades. It's pretty much one of the best DPS jobs that hapens to also heal very well. It's a king of a trade with amateurship in healing.