slask said:

So on one hand I'd love to see new stunning transfers for these three movies, on the other hand I realistically think there are not many chances of seeing state of the art HD remaster without scanning proper source material.

It has been demonstrated that the '77 35mm IB Technicolor release prints have more visible detail than what's available on the current BD.

Disney can acquire (100% of them are in the hands of collectors currently) one and use it as the basis of restoration or they can go back to one of the IP or IN prints they have lying around in the archives and use that.

There's absolutely no need to go back to the negative. It would be nice, yes, but there's enough evidence now for me to say with confidence that it's not a requirement.