Combo actions don't exist on anything that has a cast time. Playing RDM with any latency is a nightmare because you don't actually get dual cast until you finish a spell, causing it sometime fail to apply until after you start your next spell.

Also a strict rotation is incredibly unhealthy for a role that has to be able to react to incoming damage at any time. The proposed changes will see SGE either OP or in a state like Disc priests in WoW where they are actually underpowered in a lot of cases, dealing less potential damage than other healers for the same healing and a lot of work since they don't have the choice to prioritize damage over healing.