I don't think Ryo will be the new rival character. She has a crush with ANOTHER otaku, might be the person that gave her the sketchbook. That's why she knows otaku archtype very well, and become a tsun around that topic.
The second page shows that.
She become tsuntsun and self-tsukkomi herself while being shy. She told that otaku type won't date gals ever, but then quickly retracted, "That's not always true though, you know!!" It's because she want to be with that person.
Furthermore, she's also said, "Let me use you as a reference, I mean wait, no."
Because Seo is the otaku here, all her reactions fit him, but I still believe that it's a red herring. Maybe next episode we'll see the three gals basically become an alliance.
There will be a chapter of triple+double date of this otaku-gals!!
... Dang it. What a typical post of an otaku.