I've looked through the twitch-dev-discord. And there seem to be many people who like me want to use keyboard-events in their extension.

Keyboard-inputs would make a lot more interesting and fun games possible, instead of the current 5 million versions of the same quiz/sticker-extension.

Since keyboard-events are allowed in <input>, I don't understand why it isn't allowed outside of an input.

Also, I think the documentation should be clarified:
"2.3 Extensions may not use keyboard shortcuts to power functionality."

What you mean is:
"Extensions may not use keyboard input outside of a input-field to power functionality."