They managed to make the RDM spells unique compared to BLM/WHM and how they usually are in other FF games so I could see the devs managing to make Geomancer unique enough regardless if it was added as a dps or healer...or even tank (unlikely). That said they very much are CNJ/WHM similarities going on, Water/Earth/Wind being their main skills and all. Course if the playable Geomancers have a bit more focus on Water spells as far as the damaging aspect goes that could make them different enough from WHM probably.

The question is how their healing spells would work if they end up being a healer. Again if added as a playable job.