I would like the ability to create different map themes and have them all accessible from a drop down in Web AppBuilder. Different layers would activate in the map according to the selected theme. For instance, a Transportation Theme would contain all transportation layers and would turn those layers on when the theme is selected from the drop down. This configuration would also need the ability to select what layers are visible on the map by default. See snapshot below for example. This function could even exist inside a widget. The Layer List widget somewhat has this functionality but you are only able to control what layers are available in the widget as opposed to being able to control layer visibility on the map when the button is clicked.