Well, to be honest I wasn't sure how they were going to be able to pull off a special edition considering that the existence of extra footage has never really been confirmed.
All that we know is that F91 was originally to be a series or at least an OVA, but that it was changed to a movie.
IF there was unused footage, then I could see a special edition, but lacking cut scenes, director's commentary, behind the scenes, etc, all you would be left with would be maybe some soundtrack stuff, and lots of lineart and stills, which would make for a pretty lame special edition IMHO.
I just don't think there's enough source material for F91 out there.