I've been working on a very rough/early version of the co-op UI. What you see above is for creating a new player profile while playing 4 player co-op. Each player has this UI in a corner of the screen and can select a portrait and enter in a name using a game controller (so no need to fight over a keyboard or get up if you're comfortable in a chair). I designed the keyboard to be super reusable so that later on you can enter in item names or other things with it as well. Of course I'll also just let people use keyboards to enter in names and stuff too on PC.
The portraits seen here were provided by Zac Gorman who kindly offered draw some to help me with my prototyping. All the actual UI graphics I made quickly myself and are just temp art to get functionality and layout working (which is why they are flat and not very pretty/interesting right now).
I've been heavily inspired by the Destiny UI in terms of having a controller-driven cursor system. With mouse-overs it helps keep things tidy on the screen by letting you hide some information that isn't needed until you move the cursor over it. I'll be using it for item/car info boxes and stuff eventually later on.