I'm a died-in-the-wool, responsive, readable, internationalizable, accessible, standards-based, enshyenist:
Instead of using an unbreakable em dash to rigidly and unbreakably connect two phrases by their last and first words, I prefer using an en dash, followed by a shy hyphen, and then another en dash, to elegantly hyphenate words connected by em dashes when they don't fit on the line. ;)
–­–
Few fonts will render this nicely; the dashes are unlikely to join. Also if it does break at the soft hyphen, you’ve got an extraneous hyphen added on the first line.
If I were doing that, I’d probably use a zero-width space instead of a soft hyphen. Same break opportunity, removes the extraneous undesirable hyphen if it breaks, but introduces a new word boundary so that wordwise selection can now split your wonky dash. Therefore I suggest <span style=user-select:all>–​–</span> because if you’re going to do something ridiculous you might as well embrace the ridiculosity.