They wont give RDM Staff skill ever, Like it or not SE don't want them using Staves regardless the fact a few are good for RDM such as the nuking ones, just be grateful they still put RDM on the good Staff Trials.
If anything they'd only up Club skill weapon wise.
Truth be told, the only use of Staff Skill would be for Triggers in Abyssea and that's it (not that I'd mind this), no RDM in their right mind would use a staff if they planned on melee.