The biggest issue i see with Healers is literally the fact you cant really do anything much with it if you are real for a second.

You are split between People which like the 1 or 2 DPS Rotation and People which dont like it, so what will you do? Most People which dont like 1 2 will still play Healer, while people which dont want a complex rotation or anything will probably quit, so it will end in a vacuum where even more healer are missing.

So the best way in my opinion would be not to change ALL healer but maybe the half of it, give ast/sch a more complex rotation and keep sage/whm easier

and i talked to a lot of high end healer and tbh none of them actually wanted to have a complex rotation, they are fine with 1-2 so i really dont know how you would change it to make everyone happy