I started a petition to release the original director's cut of this film on DVD. If you are interested and wish for this to happen, please sign! Who knows, maybe this will help it to become a reality!
https://www.change.org/p/shout-factory-release-flowers-in-the-attic-1987-director-s-cut-on-dvd
Hey! I saw on twitter that apparently Shout! Factory (and this was directly from them) can't get the rights to it. You might have to change that petition to whomever owns the rights to it now.
https://twitter.com/Scream_Factory/status/804841111139164160
ScreamFactory is the horror section of Shout! (I went to the site and noticed the Shout Factory logo on the top left)
I've changed it to IMAGE Entertainment since, as you pointed out to me, that is the company that currently has the DVD rights to the theatrical version. Hopefully this will get the ball rolling.