I bet there might be slightly faded 70mm print lurking around out there somewhere! Warner Bros are full excuses today.
I’ve read that some rare 70mm prints have had loving tender care treatment in preserving the original channel layout onto dts70mm yes dts70mm! I found the article on West Side Story interesting read. http://www.in70mm.com/news/2010/wss/index.htm
So if they can do it with West Side Story (1961) that is an older film than Superman the movie (1978).