Problem/Motivation
In #2895124: Field storage settings give a scary red warning that they can't be changed when the cardinality is the only thing with restrictions @berdir suggested the following
And we might want a separate issue to discuss making the upload destination configurable [after data exists in a file field], because right now it's not even though there is IMHO no reason for that, if anything, we could add a description that it will only affect new files and not existing ones. See \Drupal\file\Plugin\Field\FieldType\FileItem::storageSettingsForm()
Because that issue is likely to land shortly, and that suggestion is not within its scope, this issue has been created as the new home for the idea from July 2017 that would otherwise be orphaned.
