Probably a stupid question, but what is your mechanical process? that is, how do you make entering a em-dash natural? Personally, I am of the nature that if it does not live on my keyboard I am probably not going to use the character, And I say this as a great aficionado and maintainer of a carefully curated compose key file... That I never use.

Guesses, because I like to guess, replace the dash with an em-dash? map alt+dash? compose-key dash dash dash?(my preferred method), dash dash rewrite rule(now we are getting into science fiction), ligature?