Responding here, because these other related threads are closed
Moving notes, with attachments, to new vault - Help - Obsidian Forum
Moving notes from one vault to another - Help - Obsidian Forum
If support for moving files between vaults is added, I think the attachments shouldn’t always be copied. IMO attachments should be copied to the new vault(s) when there are still files in the original vault that reference the attachment, and moved to the new vaults(s) and deleted from the original vault when there are no references to it.