This is a must for me as well! I have been playing exclusively on controller for a while as well.
I love what they did with the official support, but the lack of customization currently makes it not work for me. Even though I think it was meant as an upgrade, the targetting through directions is hard to get used to, especially when constantly moving around.
I have been just keybinding to my controller buttons and not using the Gamepad UI because of this. I do lose interaction with interface though (bags and other UI elements) which I think were done masterfully on the new support.
I think just adding toggles for some of the features and being able to customize binds and modifiers will eliminate the need for any addon or workaround for me.
One last thing for me would be to be able to keep action bars instead of the controller layout, it takes up too much space IMO, and I like the action bar look and organization on my UI.
PS: I do think it does not have much customization due to it being an alpha version. But I am fearful the unmodified buttons are something that might be a design choice.