why is the cast of the Scions so...elvish now.

[Midareyukki]

At least all my hairs still have ears!

Cool for you, enjoy them. I mean it, do enjoy them, it's one of your racial traits, you should be allowed to enjoy them as fully as possible.

Back on topic though, I don't think the problem with the Scions is that they need to expand, but more that they need to be defined. They're going to be rejoined (I forgot the word for "coming back together", this is the best I got .-.) eventually, so there might be an expansion of their numbers and diversity there.

But their previous purpose is done. The "Scions of the Seventh Dawn" are no more, because there isn't any further "Seventh Dawn" going around. They need a new purpose. And that is what will then allow for diversity, since then they'll be able to incorporate new characters better fit for their new adventure.

And possibly also retire the units that are already "done and over", like Thancred. I love the guy, and he's one of the few non-Miqo\Elezen in the group, but his arc is done, Endwalker hasn't given him anything new thus far, he really can just spend his time with Ryne once Y'shtola finds a safe way to the First.