I have some suggestions for some handy widgets:
-An embed code generator
-Export data (could integrate open data)
That is all Also, It would be great to see more customization for the themes (using my company's exact hex value color schemes)
This has so much potential, but right now it's "ability to create an app without ever coding" is very limited and I can't wait to see the development of this!
You may want to join this group here: Web AppBuilder Custom Widgets and if you have ideas you want to share, you may want to post them here: Esri Arcgis Ideas | Ideas Submission Portal
Thanks!