I expect them to remove useless spells and skill by either totally removing them from the game or doing a bit like in GW2 where the spell change everytime you press it as your progress into your combo so instead of having 3 spells for your basic rotation you'd have 1 that just change to the next one as you smash it.
I don't agree with people saying "this" would make the game too easy in the sens that smashing 1 2 3 1 2 3 1 2 3 1 2 3 doesn't much more skill than spamming 1 1 1 1 1 1
It would just free spell slot on your keyboard / controller.
Some spell could also see a great rewhole, things like Apocatastasis while good in raid are very dull. There are currently too many CD in the game with enormeous duration imo.
Also, a hard rotation isn't necearly an interesting rotation. They could make a 6 dots 8 active skill 5 out of cooldown skill rotation which could be extremly hard to master and yet dull as fuck and inninteresting.