Preview (dry-run) the document import operation

When importing documents in Administration, you risk overriding changes on existing documents that you are not aware of. It would be nice to have a preview button in the import UI for the selected documents to be imported (just like we have for document edit), that would perform a dry-run import and show you a diff view of the result (compared with the previous version, by default, but allowing to compare with other versions as well – basically, the "changes" viewer).

I find myself quite often importing a xar on a production server with the new version of (code) page content built locally (from a git/committed version), but I am never sure if under the pages that I override some uncommitted changes would exist and which I might break by my import.

The way I see it, this would be a missing feature, since it's one data input method that is currently lacking a "preview" (i.e. safety) mechanism.