The only discussion I've seen about the Hatbox Ghost has to do with the del Toro Haunted Mansion movie, not the attraction(s) at all. And all that discussion was a year ago when it was announced with a teaser trailer that featured the ghost, and del Toro said it would be a pivotal character.
He also appeared in merchandise for the DL HM's 40th anniversary.
There were rumors he would return to the DL attraction for the 40th, but that didn't happen.
The Hatbox Ghost never appeared in the WDW attraction, so it seems doubtful there would have been a space for him.