Currently in MapViewer and ArcGIS Pro, Arcade expressions can generate custom unique values based on calculations or multiple attributes. However, every time the expression is updated (even just to add or remove a value) the symbology (colors, shapes, outlines) resets and must be manually reassigned.
I'd like Arcade expressions to optionally return symbol properties such as color, shape, or outline alongside the value. This would keep symbology stable and potentially data-driven, eliminating the need to reassign styles after every expression update. As an added benefit, it would make symbology fully portable between maps - just copy the Arcade code and your styling comes with it.