Being able to define a query in Web App Builder and then allow the user to only return features that have a spatial relationship with features in another layer was a game changer in terms of the usefulness of this tool and we have used it extensively. That spatial filter option should be applied to many other widgets available in WAB such as Chart, Incident Analysis, Situational Awareness, etc.
Currently these widgets allow the user to filter results by map extent or by a drawn area, but not using a selected feature in another layer. An example would be the area defined by a power outage; it would be great to configure a chart that would return feature counts of building types in a column chart for a selected outage area. Or use the Situational Awareness widget and instead of drawing a point, line, or polygon for the incident, simply select the feature on the map (power outage, smoke plume, etc) and then return the desired Analysis Types for the specific layers.