Keeping in mind that DoW classes greatly outnumber the DoM classes, adding classes for Geomancer and Red Mage jobs would be good. Although Geomancer lore seems to tie into Conjurer lore, I don't think it's mechanically compatible.

Using the idea previously discussed revolving around altering terrain for the benefit of a Geomancer (and possibly useful in other ways as well), it sounds to me like a job for a rune caster class. And that sounds exactly how an Arcanist will play. So, it could be utilized as a secondary class allowing the Geomancer to have the ability to alter his/her own terrain as necessary. An interesting mechanic, at the least.

I suppose some form of swordmage class could open the door for both Red Mage and Geomancer.