Ship isn't sunk yet, but does the author really have the balls to go full yuri incest? At this point who knows, they keep throwing nonsense out every chapter. This twist would somewhat explain why they were so attracted to each other in a short period, but probably doesn't explain them making out after a date.
Actually, this twist amazingly didn't come out of the nowhere. Did you never think it was strange Aya and Tsuyuno making birthdays with only 1 day difference, and they becaming friends so fast?