I can conject here that the delay has something to do with who owns the rights to the film.
Not to offend Charlie (who did a wonderful job on the LEGEND DVD), but here's what I know...
The film was released by the Ladd Company through WB, and until its initial video release had distribution rights. Embassy Pictures had a financial stake in the film, and originally held the video rights. Embassy eventually released the international version on cassette and the domestic theatrical cut on LaserDisc. Embassy also held the television rights (which were passed onto Columbia Pictures Television when Embassy's TV division was sold to Coca-Cola, the then-owners of Columbia).
When the director's cut was released in 1992 or so, WB bought back the rights to "Blade Runner", but only the rights to the director's cut. WB got full rights including television and home video.
Meanwhile, as we all know, Embassy consolidated into separate companies over the years, with the theatrical division becoming Nelson Entertainment (its library eventually passing from owner to owner--DeLaurentiis, ParaFrance Communication, and finally to its current partial owner, StudioCanal) and, as I just mentioned, the TV division becoming ELP Communications (as part of Coca-Cola, and currently part of Sony Pictures Entertainment).
It is quite possible that all other versions of "Blade Runner" (including the two seminal original 1982 theatrical versions) could now be owned by MGM and StudioCanal, which is why the original theatrical versions haven't been seen in years (although WB did make available the U.S. cut to television for a short time to the Sci-Fi Channel).
If that's so, then if the legalities change, we could see a "special edition" of "Blade Runner" on DVD soon via either MGM Home Entertainment or Anchor Bay Entertainment (both have home video output deals with StudioCanal).
A 3-DVD set would be nice, as it would contain SIX versions of the film (three on each disc via seamless branching--Disc A containing the upcoming "special edition" re-edit, the San Diego Preview, and a later rough cut; Disc B containing the International Theatrical version, the U.S. theatrical version, and the 1992 director's cut; and Disc C containing the BBC "making-of" documentary, supplements, trailers, outtakes, etc.)
Hope I'm making sense of all this...