I really enjoyed Foxy´s arc in the manga and how it was expanded in the anime, so count me in for watching this special. Also, while I love timeskip redesigns, I wasn´t expecting one for Foxy at all, specially considering the guy actually makes merchandising outta his head.
As for OP needing filler right now in order to not catch up with the manga, I´d love to see
! the events of the three days since the battles were over and until the moment they ran away from Dressrosa. Really want to see how the teams were sorted and whatnot. I really liked Luffy´s "sons" and I want more of them asap, even if the interactions are anime only.