Hm... I think it's a matter of time until they do that, but I don't think it's necessarily a bad thing.
See, the thing people is scared about is condensing the 1-2-3 rotation into one button and everything else staying the same, but I feel condensing 1-2-3 buttons into one and adding new stuff to do that's not a 2 minute cooldown buff could be beneficial. Overall, the number of buttons stay largely the same, but you get to do more stuff with the same number of buttons.
Let's say you have your 1-2-3 condensed, then you can have combo buttons that can only be activated or get empowered while under step 1, step 2 or step 3. This would solve the issue healers have, because healers don't have different things to do to attack, they just have 1 button, not a condensed rotation.
RDM is a good example of this. After finishing your 1-2-3 combo, your spells flip and change to other type of spells: Instacast finishers. They feel much different from the original casted spells they substitute, and yet they don't add a single extra button to the rotation.
Using convertible "flip" spells can condense rotations greatly and still feel fun and nice to play. Heck, they could do that with 3 different buttons and make a more dynamic rotation. Something that feels closer to NIN's mudras.
Taking RDM as an example again, imagine Displacement and Engagement disappearing and being flip skills of Melee3 and Melee1 respectively. You can then add 2 more spells to the game and the number of buttons stays the same while still preserving everything the RDM had.