This is probably gonna be a biased response because I love how unique Childe's eyes are, but I don't think they'll ever change them from dark to light. They're just such a significant and defining part of his character.

But that part of the 4.1 cutscene is definitely interesting for sure. It makes me think a lot about the implications of his encounter with the narwhal and how it changed him in the past, as well as how the second encounter may have impacted him. He's quite literally Childe's constellation...makes me think about the various discussions surrounding the connection between Childe's constellation and his fate. What it means for his constellation to be a creature from outside of Teyvat.

Just kinda thinking aloud here, but I just really think that glow in Childe's eyes, that reflection of the primordial sea with its colors of the universe, is way, way more significant than people may think. Especially since there's so many unanswered questions about him.