I second that request!
Not only for use in Obdisian Notes but in all manner of Notetaking Apps this is really useful for e.g. having a todolist with (perma)links to the email that spawned that todo item. There is a standard for that in most OSes, similar to the https:// there could easily be a emclient://UNIQUEEMAILIDENTIFIER link. Ideally to be copied with a keyboard shortcut to be pasted into note taking apps. Or maybe better (at least on macOS) with applescript automation 
Currently my Inbox is my todo list which gets confusing really fast.
Also very useful for archival or crosslinking with apps like hookmark (on macOS) for example. Many other email apps implement a URI of some sort (mailspring://UID…, readdle-spark://UID…) to get to a specific mail.