Quoting myself. What if, instead of possibly complex UI needs etc.. to make this happen, tray was also a button that we could drag to any other tray as we wish. Similarly to what eg. WoW is doing with forms and stances.
That way I could put combat tray to eg. button '4' on my harvest tray. Then on button '4' I had my opener in combat tray and the switch from harvest tray to combat tray and to do attack opener would be just hitting 4 twice.
Then if we so choose we could not bind global tray switch to anything, or maybe bind just harvest tray and other trays were icons in there as harv