Lucas does save all his raw footage, so it would be possible to reconstruct the Lost Cut, and he does seem to have the whole thing as black and white and silent at the VERY least. Maybe he has the soundtrack lying around still and couldn't find it, but maybe it was damaged or lost.
Lucas certainly could release the Lost Cut in some form if he wanted to, in color in fact, since he saved all his footage .... which is why the Biggs scenes and other cut scenes are in color on Deleted Magic, of course ... but it would take some new editing. As far as we know it's not lying around somewhere perfect and ready for release. It would take a bit of work to prepare it.
There you are then.