The devs have said that it's not possible to have the "Repair All" button repair everything on your character due to how much overhead it generates for the database (or something like that). I can kinda understand that, seeing as how most MMOs don't have you carry around 400+ items, all of which could potentially need repairing.
Yet, busy players who spend lots of time in the field and queuing for dungeons with friends often need to repair multiple sets of gear, and no one likes standing there, navigating unnecessary layers of UI when they'd rather be out playing the game instead.
So how about this as a compromise...
Every time you click the "Repair All" button, the inventory space selected in the drop down menu automatically moves to the next section, with whatever delay is necessary before you can click the button again to not overwhelm the server database.
For example, you click "Repair All" on your equipped items, and instead of needing to click the drop down menu and select the next section of your inventory, it automatically cycles to "Armoury Chest (Main Hand/Off Hand)" for you, etc.
It's a simple quality of life change that reduces the number of clicks you need to repair everything you're carrying from 18 to 7. Speaking as someone who has burned out the mouse buttons on a Naga Razer, I'd appreciate the click savings, just as I'd also appreciate the time savings.
Much like how the "Recommend Gear" button isn't "necessary", neither is this change, but that's what a "quality of life" suggestion is: not vital, but makes the game experience overall more fluid and enjoyable.