Allow us to add buttons to the redactor 'insert' dropdown

[Alpha1]

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 D added the button to insert media gallery items on the main bar or if this is unrelated.
In any case: it would be very useful to be able to insert buttons there, so that we can easily add buttons without cluttering the UI.

 

[Lukas W.]

I'd love to have an API that allowed us to extend every button group and dropdown or to even hide/modify the existing buttons.