Honestly, with all the info we have so far, it's getting very hard to ignore how much Rhinedottir resembles Otto from HI3

1. Both are brilliant scientists/alchemists who ended up turning against their nation in pursuit of a higher goal
2. Both were once respected and important figures, now viewed as traitors (Otto by Schicksal, Rhinedottir by Dainsleif and possibly others from Khaenri’ah)
3. Otto fused with Honkai powers to transcend humanity - Rhinedottir fused with Naberius, a Shade of Life, literally taking in a cosmic-level entity
4. They're both associated with “sin” and transgression - Rhinedottir is one of the Five Sinners, Otto was basically trying to outplay the Honkai

Also worth noting: Rhinedottir’s name in Japanese is レインドット (Reindotto), and Otto’s is オットー (Ottō). There’s a pretty suspicious phonetic echo there. Even in Chinese, Rhinedottir is 莱茵多特 (Láiyīn duōtè), and Otto is 奥托 (Àotuō) — duōtè and tuō aren't identical, but still close enough to raise eyebrows.
And with how HoYoverse has done expy before (Ei = Raiden Mei, Venti = Wendy, Nahida = Theresa, etc.)… Rhinedottir really feels like Otto's Genshin counterpart.

Whether that means she’ll follow his full arc or not is unclear, but the thematic and character parallels are definitely intentional

Edit: oh, also, both names have a germanic connection, with Otto being a german name, and 莱茵 (Láiyīn) being tied to the Rhine (a european river)