Users can overwrite existing attachments without being aware of it

Consider the following use case:

• Alice opens in view mode the page X and looks at its attachments. The list is empty.
• In the mean time Bob opens the same page in view mode and checks the attachment list also
• Bob uploads image.png
• Alice uploads her version of image.png without being aware that she is overwriting Bob's version

Ideally Alice should be notified that the page has been updated (especially the attachment list) since she opened the page.