Essentials are foundational subjects that have the highest probability of preparing a student to become more productive and useful to society. So your question about required versus elective courses centers around 1) what society collectively decides is useful and 2) what a student at a certain level can practically grasp and grow from. I think we'd both agree reading is an essential by this definition but truthfully socially and communally controlled influences make these decisions (thing like the economy, elections, and enrollment) not you or me.
The problem with discussing this on a forum on HN is that we're all biased. We all think programming is incredibly important to society because its incredibly important in our lives personally. If you go onto any forum where everyone has a collective interest, they'll all say subject A should absolutely be taught in school because of X, Y and Z. Truth be told on a macro scale every skilled field is battling for the attention of capable students to eventually join their ranks.
I think what many on HN are missing is that if your going to introduce programming (especially as a core subject) into formal education, you'll need to sacrifice other subjects to make room with the way education budgets work. Of course everyone is going to say something like oh well you should cut down on art, music, social studies etc but its not a helpful perspective unless expressed in a truly diverse forum.
If that's the case, which subjects are the "essentials" that should be 'required' and which ones are 'elective'?
I'm not sure I think coding is up there with reading, or arithmetic... But it's probably more important than some currently required subjects.