As a fan of being able to declare my symbols directly from XAML, I've implemented an extended PictureMarkerSymbol to support this. As a side benefit, I ended up being able to set the symbol from any ImageSource, including DrawingImage. This provides me with the ability to define symbols from Path or other geometries to create richer symbols, without having to create my own fonts, and still make things scale.
I realize too rich symbols may cause clutter in the map, so it is still important to keep it simple. If anyone sees a problem with this implementation (like it won't be supported in the future), points of improvement, or anything else, please let me know.