I know that Ysera is back. Old news, I’m sure we’ve all seen the video, but I haven’t done all those quests yet so…
When I saw the new aspect cinematic today with all 5 of them together, it had Merithra. Now correct me if I’m wrong but Ysera was brought back to lead the green dragonflight right?
Or… is she just back? Is Merithra the green aspect now? I’m confused.
Edit: Thanks for Clarification
I don’t think Ysera is intended to be back forever.
Merithra is the green aspect now as per one of the Valdrakken accord questline. Ysera is just here on a…temporary exchange basis.
Merithra is the Green Aspect, Ysera is just a dragon emeritus, helping out when she can.
Yes.
Yes.
Ysera is no longer connected to the Dream as she once was due to being an Order/Death Hybrid entity so Merithra who is more connected to the Dream than her Mother must become the Aspect of the Dream in her Mother’s stead.
Ysera is now a being of Ardenweald and the Dream which in the case of the Dream weakens her connection to it.
She is too impure to command the Emerald Dream just as the Winter Queen would be too impure to command Ardenweald if she were temporarily disconnected and infused with the Emerald Dream’s power.
Ysera comes back for a few quests and then you never see her again. No idea why she needed a new model for that.
Presumably she was going to come back on a more permanent basis but people complained and said it should be her daughter leading the flight. Whether they always intended Merithra to be leader or not will probably remain a mystery but regardless I am glad they made her the new leader.
Warcraft needs to keep moving forward.
Probably the artists just wanted to draw more dragons. 
Ysera was restored by the Winter Queen in SL. She can not reincarnate in Azeroth.
They traded Malfurion for her but even so her connection to the Emerald Dream is now weakened and so her Daughter Merithra(who still has a strong connection to the Emerald Dream) must take her place as Aspect of the Dream.