Well, they have Hocus Pocus at the Halloween Party at WDW so maybe - though adding all 3 Sanderson sisters seems like a lot.
Headless Hroseman would be cool - even as like an add to the parade as he comes out first before the Halloween parade. And maybe some Haunted Mansion decorations - the ghosts, the ghost hurst, etc
Oh, and did you mean Madam Leota?
Not sure what other attractions they could do that are Haloween related
I know in the Family Guy game like this they have decorations for the houses (so like Halloween or Christmas) which function similar to the character costumes in this game. Wonder if they could do something like that and have haloween version of Mickey's house, etc