Web AppBuilder in ArcGIS Online March update mainly targets support for accessibility. Twenty-one widgets and five themes have been enhanced for this feature, including selected screen readers. With the incremental releases, more widgets and themes will add on to the accessibility list.
In addition, the new Network Trace widget enables you to use a geoprocessing service to trace a geometric network and interact with the results. When sharing a link or a URL to an app, you now can control which layers are visible with a new link option in the Share widget or with a new URL parameter, showlayers. See the blog below.