It technically has been done already, though not in a fan capacity. The very first edition of the Dark Crystal on DVD actually had an isolated score track in excellent 5.1, which is why I sought it out after buying that box-y edition. The new 25th Anniversary Edition that they just announced doesn't have the isolated score track either, and I don't know why. It's rather irritating, as it's a beautiful score. Maybe a release of the movie with just this original isolated score track would be in order?

And that limited edition OST is a beaut, isn't it?