In the past we were able to add animations to specific features by using animated SVGs as the icon. It seems like there is a known limitation for animated SVGs. The PictureMarkerSymbol class documentation says, "Animated SVG images are currently not supported."
We'd love to know if this is a planned feature that is upcoming, or if it's currently unplanned. We might have to segway to using GIFs, but obviously that's less than an ideal workaround for animated SVGs. Also wondering if anyone has experience with working around this.