The basic problem here is that if this goes through, from then on, everyone will think Dark Shadows is a movie.
Same way as if I mention Carlo Collodi's magnificent novel Pinnochio people immediately shift the conversation to a cartoon Disney made. Same way as it's impossible to talk about L. Frank Baum's masterwork without people hijacking the conversation and talking about an MGM movie with Judy Garland (who resembled Dorothy Gale in no way I can think of, other than being female and boring).
If they make Dark Shadows a movie, the odds of anyone ever knowing what it actually is again drop right down to nil, and that's sad.