I agree, the action menu / scroll wheel menu should appear in the layout editor.
I have somehow managed to move it a long time ago, I wasn't aware at the time that it was not a feature of the game.
I found out the hard way today when my layout got wiped due to there not being a save function. In trying to recreate it, I realized that the action menu was missing in the layout editor.
there is visual proof that I made it work, and I can attest to the fact that it was persistent even in vanilla arma. I am very curious to know why I was able to do so in the past and not anymore

Replying to this with further insight:
It appears that most, if not all, of keybinds labelled "Toggle" only function if the key is pressed twice quickly. This is the case here.