Considering I've seen hundreds of blank Twitter posts, no, I don't think they necessarily would. Even ones that aren't blank don't necessarily say who the character is.
I personally don't think it's Illya. No hard evidence but Illya has a part in her hair on the side that the character is facing which is missing here, this character's hair looks like it's definitely suppose to be blonde whether than platinum that looks blonde and finally this artist has drawn a similar looking red eyed blonde before.
