I don't see Ritualists replacing Monks, but they can definitely play supporting roles. Ritualist healers are to Monks what Fire Nukers are to Air Spikers: they provide a nice AoE effect, but not enough to complete the job. By themselves they're not very effective, but they can certainly provide very effective backup! In the PvP event, I had a Ritualist healer build that generally maintained everyone's health at a high level, but I was unable to counteract spikers. With a good healer in the group, though, my teams were pretty much invincible.