Imagine that, a daughter looking very similar to her mother.
It's also not identical. The crescent isn't the same crescent, it's a new smaller more elongated one. The hair isn't Ysera's typical high ponytail, it's a longer, thicker braided style. The eye marking aren't Yseras (merithra doesn't have consistent markings), the skin color isn't the same, and perhaps more improtantly, unlike the other four who all have outfits directly in line with/updated from their previous versions--the green dragon here is wearing an outfit that is absolutely nothing like Ysera's previous clothing in shape, style, or color.
Ysera was specifically soulbound to Ardenweald and can't leave without "a great sacrifice". She also phrases her potential return as a "one day" thing. They're not going to bring her back 1-2 patches later. Follow the simple story beats, guys. They've been building Merithra as someone struggling to step into her mother's role for a couple expansions now, and Ysera was firmly sidelined.
is Danuser's exact description of the green flight's story in Dragonflight. The answer to who Merithra is and her difficulties living up to her Mother's role are not going to be "Ysera comes back and retakes her place, and Merithra goes back to not having to worry about anything and is just a dragon".They lost their Aspect, Ysera being killed in Legion--and now she is in Ardenweald, in the Shadowlands, and she remains bound there. So her daughter, Merithra, has had to try to take up some of that mantle and lead, but she faces questions about herself and her role as well. So the green flight has a lot of things to answer and explore in their legacy.
It is very likely just Merithra's new model, given actual similar horns to her mother rather than default demon hunter asset horns, given a proper dragon eye glow like Alex and Nozdormu instead of the generic night elf one, and given a crescent similar to her mother's.