What are your best ideas to automate metadata management

SharePoint is great at ingesting content but uploading content without metadata effectively means you are using SharePoint as a web-based file share. One area where there is room for improvement is in the area of metadata.
Caching of previously entered metadata is not supported out-of-the-box eventhough it will greatly simplify the user' task. 3rd party solutions are emerging with the capability. See https://directory.collab365.community/office365-sharepoint/best-document-management-tools-for-sharepoint/
For example, my company has developed a browser-based tool named SLIM Companion Explorer that enhances metadata support (e.g. caches content-types used, map source properties, ...). Being able to re-use metadata in SharePoint whether it is retaining the original modify date, extracting a property from a PDF file, capturing the email subject, .. is going to be key.