I think we can all agree that the PvP in Guild Wars 2 is shaped for the tactically good players and thank god for that :-) Its critical to keep track on cooldowns/buff and debuffs at all times when fighting. I have noticed that several Rune sets have internal cooldowns on various passive abilities that procs when X event happens. I think it would be really cool to be able to monitor the cooldown on these abilities. Like adding an icon on the UI where you can monitor these abilities.
On a different matter it would be cool to have a quickbar (maybe on the right hand side) for consumables/blueprints and the likes. Items that you have to open your inventory to use.