Correct - the option to use XAML for symbols has been deprecated as it was causing very severe performance issues, and wasn't a sharable symbol type across the ArcGIS System.
You can use a PictureMarkerSymbol to display anything you want (as long as you can generate the picture - there's plenty of tools and APIs that can do this), or perhaps the CompositeSymbol might be able to do what you need (ie compose a TextSymbol on top of a SimpleMarkerSymbol to create a symbol with a number on it etc)