Very expensive. Even the DVD was a problem as they had dumped all the original files. CGI source files was several warehouses. Too expensive to keep. This also problem with scanning film at 4K and downsampling for DVD. When BluRay came along most of the raw 4K scans had been trashed. The live parts (film) of PAL Region DVD are thus higher quality than the CGI parts already! Not so noticeable on Region1 DVD (480 lines vs 576 lines in PAL Regions). I think they only had the TV station distribution tapes for the CGI parts.
Actual 4K or UHD needs even higher resolution scans. Basically you need always to sample at twice the vertical and horizontal resolutions of your destination to avoid jaggies and aliasing effects such as Moire fringing etc.
Disappointing