Well the em dash remains difficult to type on a normal keyboard, this is a major reason why I don't use it, and why I think it will never get widespread adoption
(One might feel that normal keyboards don't have a compose key.)
On the other hand, normal keyboard have an insert key which serves no purpose and can thus be remapped to compose.
Not on Mac:
hyphen/dash: -
En-dash: ⌥-
Em-dash: ⇧⌥-