• Ukelele keyboard editor
• macOS system text replacement
(In my set‐up, “∈” is 3 keystrokes, “contains” is 8. Someday I’ll get around to releasing it to the world.)
But you are correct that there is immense community resistance against accepting anything from outside ASCII into the language or standard library. It was not a realistic pitch, just an extension suggestion for anyone else so inclined.