Your particular example wouldn't be deterred from the tactics that Elon says that he used, though. If it's not leaked to the public it wouldn't be seen by those that encoded an identifier into it.
But it would be discoverable and traceable in the case of legal proceedings.
If they kept the original correspondence then it would anyway. Plus this wouldn't be legally binding in a court room when Elon runs in and is like "I think the spaces match the one that I sent to this employee." That is not enough evidence to say that the employee did it when it is trivial for the ploy to be subverted by another employee just inserting a space in a random place.
defense in layers. no single mechanism wins the trophy.
Shaming tactics are orthogonal to defense, especially when the only way this succeeds is when nobody thinks the CEO is paranoid enough to try it. If anyone is leaking private memos from an Elon company now, it is trivial to disrupt this by reformatting the document and rephrasing sentences.