RPR Material Nodes lack the option to use Image Sequences as a changing mask over time.
e.g. If you use Blenders Dynamic Paint feature to export a black and white Wet Map for an animation this can usually be used to mask the area that will become the wet part of the material. (see this YouTube for a full example Creating Realistic Wetmaps in Blender CGC Weekly #20 - YouTube )
Similarly if using the excellent Adobe Character app to generate a transparent PNG sequence of a lip sync you cannot render the "Image Sequence" over a material applied to an animated character face when using RPR in Blender.
Feature request: Image Sequence input node for materials.