This is an excellent idea! As an Esri business partner with a widget, I find that our customers are challenged with finding a place to deploy their applications that include our widget. A related idea (not sure it's different enough to submit it separately or how feasible it is for that matter) is for Esri to write into Web AppBuilder a way for those who write widgets to host a widget on their own web infrastructure and provide a way for ArcGIS Online users to consume a widget as a service via the online Web AppBuilder.
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