There is still no digital storage system today guaranteed as a more effective long-term solution than celluloid.
In large digital archives the impending problem of data loss forces a whole series of precautionary measures. Archivists have to make multiple copies of large amounts of data, and maintain these copies in several locations, checking each one regularly for errors. As if this wasn’t enough they have to keep abreast of the latest developments in computer technology, and be trained in its use.
All this could not be further from the film conservation practices of the past. As the source materials were on film, archivists worked on how they could be stored in cold, dry vaults. If films are kept at low temperatures and in low humidity, they last for hundreds of years.
There is another reason major film studios still archive their features on celluloid. The file sizes of a feature production are so colossal that the migration of digital data - the copying from old file formats to new ones - can take an extremely long time.
Digital archiving has however re-established itself with the inception of the first open-source format, the FFV1. Before then the most commonly used format , the digital picture exchange (.dpx), had multiple end details, such as colour encoding, which were selected in the final stages of post-production. When it comes to viewing films stored as .dpx files in the distant future, this will depend on whether the archivist knows how they were digitally packaged, and if they still have the computer hardware and software to open them.
For a summary of the current practice see Andy Maltz's 2015 article Will today's digital movies exist in 100 years?
Two landmark reports by the Science and Technology Council of the Academy of Motion Picture Arts and Sciences:
The digital dilemma (2007) how key players in the movie industry have set about storing and accessing digital data
The digital dilemma 2 (2012) the challenges faced by independent filmmakers, documentarians and non-profit audiovisual archives