It would be nice if you can set a folder to upload/copy new file uploads to multiple storage locations.
For example if you upload to “photos” it could use the external storage application and upload those files to Wasabi S3 and another remote Nextcloud folder, while keeping a local copy on the Nextcloud instance.
Basically just an easier way to keep multiple copies of your data using the 3-2-1 backup method.
Thinking of it, git-annex was such a solution where you can add different kind of storages (local drives, usb storage, ssh-storage, …) and you can somehow define on how many different drives your files should be synced. And some storage can just be temporarily attached (e.g. usb drive): https://git-annex.branchable.com/walkthrough/