I think it makes a lot of sense that Mattel and the 4 Horsemen are taking Mark Taylor's version as a point of departure. They should start off from their own original vision and not from Filmation's watered down derivative. It's not because millions of people watched the cartoon and less than a million ever owned the actual playset that the Filmation version would be the more iconic one. I'm quite certain that most of the people who watched the TV series won't remember exactly what Castle Grayskull's teeth or the shape of its eyes looked like, they will merely remember that it was a green castle with a big skull in front.
Besides, the Pre-Filmation fans and the vintage fans are more or less on the same page when it comes to Castle Grayskull's visuals. Filmation, however, is a total departure.