I don’t think a confession would necessarily come as a complete surprise to Touko—that confrontation on the rooftop, while not directly romantic, certainly indicated Yuu’s emotional intensity toward Touko. The question of how that confession would be received, though, depends on several things we don’t yet know.
Hypothesis #1: Touko is totally cured of her “Faking My Sister, Hating Myself” syndrome. Now the question becomes: how much did Touko’s (what I have called) “Sudden Onset Yuu-itis” depend on that syndrome? The relationship was introduced as a sort of “practice love” that Touko valued because it was something she thought she would never feel, and Yuu was safe as an object of affection since she would (supposedly) never reciprocate Touko’s feelings. The relationship has become much more than that, of course, but it’s still an open question what will happen when the “in love with Yuu” app resets under Touko’s new emotional operating system.
Hypothesis #2: Touko is still tied to some extent to the old dynamic with Yuu, so a confession is received as a (“betrayal” is too strong a word, but something like breaking their long-term contract)—she might see Yuu as having been duplicitous about their relationship (and in a sense she wouldn’t be wrong.) Touko was awfully ferocious about the “don’t love me” part, and there’s a chance that Touko might now discover that what she calls “love” has turned into gratitude and friendly affection. (We might call this the “Now that Yuu wants me to jump her bones do I still want to?” question.)
I think a bad end along the lines of #2 is extremely unlikely—it’s theoretically possible, but just not aligned with the trajectory of the story as a whole.
I expect there will be some type of less-than-complete understanding between the two of them before the end. In fact, as I’ve mentioned, I’d be a little disappointed if there weren’t something, because the story has treated the issues too seriously all along to end with a quick greeting-card play-as-miracle-cure and all’s-well, hearts-and-flowers finale. Touko is suddenly seeing herself in a whole new light, and a confession would require her to see Yuu (or rather, to see that Yuu sees her) in a whole new light. Some authors would have that happen with a snap of the fingers, but I don’t see this one doing it.
