There are many layers to this problem, depending on your playstyle and the playstyle of those you move through various aspects of the game with -- your perspective changes.

I still see many healers who don't hit the DPS buttons that are in place now. A good number of them. I've worked with players who get stressed over the complication of DPS on top of Healing. These are your casual healing purists. Complicating healing further creates more stress here.

I still hear complaints from some DPS and Tanks when going full glare mage mode and they aren't riding 100% health. I hear it from other healers as well. "Aren't you going to heal?" I've hit as many buttons, likely more... I'm using my oGCD and see the other healer still attempting to proc cure 1. Adding more buttons to slow down the average player still creates stress here. There was a post pages back about returning to the rotation after movement or emergency heals. They happen.

Stronger players, especially when playing with other strong players... Yes, this can get boring and dull, especially in standard content with some fairly skilled tanks being able to heal themselves entirely. Dia, Glare .... Holy SPAM... Help is needed for the brain numbing which happens. I have friends who will only see benediction, or the obligatory "git gud" regen when they reflex check me. These aren't the players that you tend to run across day to day.

This is where everyone splits. The answer isn't just to complicate the DPS rotation for healers. In general, for two sets of players, this will make the job more undesirable or cause problems for others. It doesn't really fit in to the idea of "Casual Gaming". In harder content, there is a place for it. Better ways to help the party.

The old FFXI had something here, sub jobs. Not favorable, again because of casual play. Players essentially were /forced/ to level specific jobs to augment their main.

What if there were a way to pull in one or two abilities from another job you've leveled? Leylines before Misery or Holy Spam... Game on.