I do not know if this has been suggested, or if there is a way to implement it currently, so here goes...
I think that the action bar should not be a bar so much as a 3x3 square. the default button should be the center button, which if you are using a controller after selecting an action to perform the selection box will return to this button.
Alternatively, setting it up like this would allow you to use the D-pad on your controller directly to select an action and have the box "snap" back to the center as soon as pressure on the d-pad is removed.
I just find it to be a "quality of life" change that would not affect keyboard users and would help streamline the controller useage. By having every action on your bar within two directional presses away (or alternatively using the d-pad) would allow people to focus less on their action bar and more on the action of the game.
Anyway, could just be a personal wish... if its worth posting to SE, someone with the means or motivation please do so.