I'd love for people to pick up various members of Illya's family, it doesn't particularly matter from which canon point... But it should be noted that at Illya's current state, her opinion of Shirou and Kiritsugu is very negative. Kiritsugu she believes has abandoned her, while she sees Shirou as the person he abandoned her for.

Iri is probably the only one of her family that she wouldn't want to cause harm, but seeing her would be a rather emotional experience all the same. She died when Illya was very young, so her emotions would probably explode if they ever met.

Then there's Archer, who Illya doesn't even know is a future version of Shirou. I'd love to see them interact, seen as canonically Archer is said to have a particular fondness for her, and in his timeline she survived past the Grail War to die only a year later, apparently. Seeing them interact doesn't happen much in canon, so a chance to play it out is something I'm always happy to have.