In LOTRO I use an add-on that adds collapsible, configurable hotbars (for instance, a vertical bar that lets me hover over my favorite mount to have a horizontal bar extend out showing other mounts, or hover over my Return Home skill to have a bar extend out showing all my instant travel skills, etc.) An equivalent would be just as useful here. I use another add-on that lets me keep track of the inventory held by all my other characters, as well as see what's in my Vault (think Retainer inventory for FFXIV equivalent) when I'm not there. That one may not have as wide-spread of an appeal here where fewer players have multiple characters, but it would still be useful for those of us who do. I've seen some that show hotbar skills/items only under the specific circumstances that make them useful (equivalent here would be, for example, a WHM who only has Esuna pop up on their hotbar when a teammate gets a debuf they should dispel). I wrote a plugin myself to let me allocate several currencies between my alts which the game itself treats as account-wide but I preferred to treat as belonging to specific characters. There doesn't seem to be any direct correlation to that here, except in the very broad sense that it allowed me to take a feature and present it differently than how the basic game presented it, making the game as a whole more customizable. There's all kinds of things you can do with them.

The only downside to add-ons in this game is the fact that it's cross-platform, and the add-ons would almost certainly be limited to PC-only. (The people trying to claim that PC beats any other platform you can play on would finally be right, and that's not a good thing for a cross-platform game.)