Thanks again Morten. The ArcGISHttpClientHandler may be another option.
So really my fundamental requirement isn't as technically complex as the current solution was made to be. My user will have a collection of data and they will want to select many items from their collection for display on the map. The application would build an image based on the selection and draw it over the basemap in the correct location. For some of that data its simple geometry which I'm having no problem accomplishing on the GraphicsOverlay. For other data we are creating bitmaps that have to be drawn on the screen for various reasons. In one case we have very large volumes of 3D data and we want to take one particular horizontal slice of that volume, create a bitmap, and display it on the map. For this one an example might be a high resolution map of all temp values in a state for instance. You'd want to overlay the entire state with a color matching the temp value at that particular pixel for the entire state(assuming you had such detailed measurements all over the state). In another case we are allowing some custom annotation where a point might be represented by one of several symbols depending on the status of that entity and then have user determined labels to the left, right, top, or bottom of the symbol based on fields selected by the user. There is another layer that did some custom annotation where the code is making use of raster graphics to accomplish the goal. I hope this helps explain a bit about what we're trying to do here. I don't think it's incredibly complicated but I am having a hard time converting the existing code to the new runtime.
I was able to get a sample GeoTIFF and display it on our map just statically referencing it. So the raster feature there works. But when I try to take the MemoryStream that contained the bitmap image that we were generating before, copy it to a FileStream, and then later replace that GeoTIFF with the file on disk it doesn't show up.