Hekili has an option where you can choose how many windows you want, so you can see the spells next few spells that needs to be cast.

Is this possible with Aethy?

I think its a big deal, as it would make room for more flow in the rotation, because you know what the next spell needs to be.
It kinda stops the fluidity of the rotation if you have a class with alot of instants, as it would require alot of focus on the addon itself. A second or even third window would just be neat.

This is currently not possible due to how things are designed.
We considered this question (of prediction) multiple times, and we decided it's not something realistically reliable.