Any chance we'll ever be able to specify an icon or FontImageSource as the source for a RuntimeImage... specifically to use as the ButtonImage in a callout?
One of the challenges with this is that the API used to define the button image is in our cross-platform parts that are separate from the UI framework packages, which means there are no such thing as an ImageSource at that level. That's why we rely on the RuntimeImage as a cross-platform image object.
Having said that, a RuntimeImage is just another bitmap, and you can generate bitmaps from those image sources by using `Esri.ArcGISRuntime.UI.RuntimeImageExtensions.ToRuntimeImageAsync`.
But I hear you and can see the benefit from being able to use UI specific sources that might even be vector-based, so I'll refrain from saying this'll never happen, and have a think about how we could potentially allow this.