Alot of really good ideas here. Although im not a RDM by any means i did have an idea for them i thought might work. What if they had an ability (not a spell) that would allow them to casr in the middle of a combo without interrupting it. For instance, rdm does tier one ws, pops ability, casts a cure or debuff, then continues on with combo.

I dont think this would be op only because i think the timer for the combo should stay going. That would require the player to have to be quick about choices and it would also prevent them from casting high level spells as they have longer casting times. Basically theyd have to be able to pull off the ability, cast and still have time to pop the second ws to keep the combo going.