I think raising the skill ceiling for healers is actually the play, but begrudgingly, not through healing.
Imo class design is at it's best when something has a low skill floor and a high skill ceiling. You can pick up the class and play it to success with minimal effort/knowledge, but if you want to excel, you have room to grow. Since healing is so binary, either someone is gamer enough to keep up with the incoming damage, or not; the skill floor has to be low in order to not dissuade people from the role. So with that restriction, the next best bet would be to give healers a more comprehensive and engaging damage rotation. The devs already design non-savage/ultimate content around healers not doing any damage, so I fail to see why they wouldn't try to at least give healers more than 2~3 buttons to press.
It doesn't have to be a casual vs hard-core debate if both can get what they want out of the job. Healer damage might not be what folks exactly want in order to make it happen, but it's the best I can think of that isn't just telling newer healers to drop their canes in the name of the role being made more interesting/difficult, or telling raiding healers that they should play a different game or switch roles.