redactor buttons

I see that addon developers have difficulty to add buttons to the 'insert' redactor dropdown. Developers need to add buttons to the main redactor bar, which clutters the bar over multiple lines with both essential as non-essential (but still handy) buttons. I am not sure if that's why @Chris...

Any chance of extending the dropdown shown above? I've tried to map some code examples from around to solve the problem, but the closest I got was positioning the button next to the 'Insert' button.