What we know about Illya's route
>Nasu confirmed that Ilya's bird familiars were from the draft
>Nasu: If it's at the land that houses the Holy Grail, then Ilya is indeed that strong. And being able to make a familiar from her hair was in the original draft. The work this time around was especially hard, so I ended up using an "Iri's replacement" approach. By the way, the name of the technique is Elfen Lied [German for Elves' Song, 天使の詩 - Angel's Poem]. The bird's name is Storch Fieseler [German term for a type of plane].
>Takeuchi confirmed that Shirou would have a sex scene with Leysritt and Sella
>At the initial concept stage, the only details we had hammered down about these two maids were their names, their general roles (powerhouse/teacher) and which one would become Illya's Dress of Heaven. We only expanded on these characters when we decided to go ahead with "hollow". Normal homonculi are mostly emotionless like Leysritt, so that illustrates what a unique case Illya is. Leysritt was created as a sample of Illya, and Sella was allowed to live only because she was useful as Illya's tutor. That's about the extent of the specifics we initially had for these characters. When I started writing Sella's part in "hollow", however, she quickly became one of my favourite characters. I like Leysritt too, of course. By the way, I think Sella is the only real tsundere character in "Fate". (laughs)
>Shirou losing his arm protecting Ilya, the two shopping and her singing, BRING ILLYA BACK, and Nine Lives Revolver were also planned for Illya's route
>Shirou was going to drop his ideal to make amends for Kiritsugu's sins in Illya's route, while the Sakura route focuses on him breaking free of Kiritsugu and becoming his own person. Also, Rin was likely going to become a villain after killing Sakura and going mad in the Illya route to complete the pattern of how each heroine is a villain in some route
>Zouken was the final boss