At the moment there are a bunch of pre-cooked configurable web application templates in Portal/ArcGIS Online. However they all look completely different with different UI customisation options. It'd be great if there was a selection of themes/colour schemes interface styles that could be applied across all the different web app templates so they would look the same and provide a consistent experience for the user.
So creating a web app from a template could be a two step process: choose functionality and then choose theme. Or the ability to import a theme from another web app if you have made changes would be good too.