The movie could theoretically be released on DVD, if someone can be bothered to work out all the legalities of getting the footage of all the different bands cleared.
But an "expanded" edition is impossible. In one of the Grateful Dead books I have, it's said that the director had filmed entire performances by the various bands, and had always intended to make a sequel, but could never get funding to do so. He carried this footage around with him, every time he moved, but eventually reached a point during the 80's when he could no longer afford to pay for the storage fees. So he was forced to junk all of his outtake footage.
But an "expanded" edition is impossible. In one of the Grateful Dead books I have, it's said that the director had filmed entire performances by the various bands, and had always intended to make a sequel, but could never get funding to do so. He carried this footage around with him, every time he moved, but eventually reached a point during the 80's when he could no longer afford to pay for the storage fees. So he was forced to junk all of his outtake footage.