ArcGIS Online has come a long way in recent years and a major reason for that is the support for Arcade expressions. While the advancements have been many, one key gap that still remains is the ability to create a Feature Set item from an expression. This would be similar to creating a hosted feature service, but instead it would be a read-only feature set. This item could be added to web maps, and treated as a layer or table. The resulting layer/table views could then be used for widgets such as query, filters, etc. While some of this capability can be engineered at the application level (e.g. Dashboards supporting Feature Set return objects to populate widgets), there is no way of saving the resulting feature set for later use in other applications.
The user process would be very straight forward. On the Content page, the "Add Item" dialog would include an option to create a New Feature Set. When selecting this option, an Arcade Editor would display, allowing the user to define the Feature Set definition. A user could then author the expression to return a Feature Set, and then a new item is created in their content, similar to a new feature layer. The creator experience could be further advanced with dialog prompts to define a desired schema, geometry type, CRS, etc. Now the user can add this item to multiple web maps, reference in applications, etc.
