Good text. I'm far less concerned about mono compatibility than I was 30+ years ago cutting vinyl. Back then you could get a cutter head to jump out of the grooves.
These days you may get more cancellations, but the music still plays.
The destination is also a factor. In a theater, you want everyone in the room to be able to hear a decent soundtrack. Listening positions are everywhere so it all has to work everywhere. FM is less of a factor now due to digital transmission of TV and other factors (satelllite radio, web radio, etc.) AM radio is stereo here in the USA.
Most pop music releases are now played on headphones. Hi-fi's with speakers have never been this uncommon in my life. Rather than everyone gathering in a room to hear a recording, everyone has their own player and ear-buds, that's when they arn't staring at their dumb phones. Music listening has become a solo experience. It's like watching a modern family out for a weekend dinner. They all sit quietly staring at their phones with ear-buds on while I'm left wondering if they acknowledge each other's existence.
With the low fi acceptance of bit reduced audio, I'm less concerned about mono compatibility than I have ever been. Digital delivery does offer the mixer more options, including psycho-acoustic tricks to move things about that would never get cut to vinyl. I see nothing wrong with a non-mono compatible stereo recording that offers the listener extra sonics that would be missed if they were forced to conform to mono compatibility. A warning on the label would be fine for me.
WARNING: This recording is not compatible on monaural playback systems. For best results, only play on stereophonic playback systems.
The one warning I want more but will never see is:
WARNING: This recording contains excess distortion, digital overs and mass compression. Listening to this product may cause insanity, loss of bodily functions and a tendency to beat your spouse.