Realistically, what’s keeping Disney from releasing the OOT? Costs? Low interest? But I’d argue that, since we know they’re already scanning every negative, even deleted scenes (see Rogue One), they may as well have scanned all of the original trilogy at this point, anyway. And even if they don’t find printing new discs worth the costs, they could release it as a digital download: granted, it’s not the same, but it’s a viable solution that would cost them virtually nothing.
So, I don’t think these are the problems. I think they just don’t want to release it at this point, probably because they want to focus on marketing the new movies.