There will only be a problem if existing tanks and healers swap permanently to SAM/RDM... Anecdotal evidence, yeah, but the ones I know who play those roles seriously as their "main" have no interest in either of the two new jobs beyond leveling them for completion. Most of my tank and heal buddies are excited at the prospective re-balancing we're going to get, rather than spiteful and seeking to "punish" DPS mains.