Wish: restrict access to some files within a dataset using private URL

[vkush]

Currently via the "private URL" (or "preview URL" since v6.5) option we can provide access to entire not yet published dataset - all files within the dataset will be visible (preview + download). But for some cases is needed to close access to some specific files (e.g. via "restricted files") even for journal reviewers and publishers. This is currently not possible (see comment here and here, restricted files will be always fully accessible via private URL), maybe we have to create a feature request for that.