I think it may improve the gamepad experience if the most recently pressed/held shoulder trigger or shoulder button always takes precedence over any that are already being held. I feel it would be a more consistent (and quicker and easier) behavior than how the buttons and triggers currently interact.
As far as I'm aware, this would not conflict with currently existing functionality.
As an example of how this would work, when switching hotbars between skill use (this would also apply when changing target modes), compared to the current behavior:
Current behavior
1) Use skill on one hotbar.
2) Release hotbar trigger.
3) Hold hotbar-cycle button.
4) Press button to select other hotbar.
5) Release hotbar-cycle button.
6) Hold hotbar trigger.
7) Use skill on newly selected hotbar.
Proposed
1) Use skill on one hotbar.
2) Hold hotbar-cycle button.
3) Press button to select other hotbar.
4) Release hotbar-cycle button.
5) Use skill on newly selected hotbar.