The update for Cure III / IV was nice for anyone not a WHM. For WHM's it made your healing cheaper overall. Your still not going to be replaced by a RDM, might be with a SCH in extreme situations. For big damage that is what Cure V is for. Cure VI is worthless currently.

Cure V / VI need some special effect to make them more attractive. I would think they would be given a higher cureskin cap and longer duration (60s vs 30s). Also give WHM Erase II which would be capable of removing multiple status effects at once.