Ability to have a WebApp Builder site work without ArcGIS Online. There is the LocalLayers widget. I would prefer to use an official solution however for my Emergency Operations viewer, vs a 3rd party widget, for something so critical. As the internet may go down or AGOL may go down. That would get Esri in to a lot more places as well, that have security as the first requirement; DoD, utilities, emergency operations, mobile work operations, etc. Having a WAB viewer that works entirely on premise without needing AGOL would allow for its use in these situations.