Go look in your game folders. Pleeeenty of widget files in there. For instance:
ActionGuageWidget.tpl/.form
MiniMapWidget.tpl/.form
TargetSelectModeWidget.tpl/.form
ItemSearchListWidget.tpl/.form
Bolded = added after launch

So as it seems, the UI is ready for it, it's just a matter of SE flipping the switch on for customs. Though with the future UI changes, they probably won't until after that.