I have a use-case where (point) features need to be drawn with a complicated symbol, that cannot be configured in ArcGIS. The symbol depends on a number of attribute values from a related table, and in theory, every feature could have a unique symbol. Symbols need to be updated whenever an attribute value changes.
My idea is to generate images of the symbols whenever an attribute value is updated, and store those images in a web-accessible location. The layer renderer would then need picture markers with a (possibly unique) URL for every feature.
This would probably be an easy task when using the JavaScript API, one could write a custom renderer that does just that. However, it would be cool if it is supported out of the box, and not just with the JavaScript API, but everywhere.
To do this, I imagine a PictureMarkerSymbol could be used, but the URL should allow for fieldname substitution, e.g. https://example.com/images/{OBJECTID}.png would result in https://example.com/images/12345.png
This approach could also be used for any classified renderer, so rather than generating the classes beforehand, we would have a more flexible way to do that.