Thank you all for the feedback! I probably should have been more specific. I have utilized the MapImageLayer functionality in 3.x for overlaying a local georeferenced image with success, but I noticed that same functionality doesn't exist yet in 4.x. According to the ESRI functionality matrix the 3.x MapImageLayer has not been implemented in 4.x, since the 4.x MapImageLayer actually is a conversion of the 3.x ArcGISDynamicMapServiceLayer.
So I guess the main question that I was asking if anyone had figured out a workaround to achieve the 3.x MapImageLayer functionality utilizing the 4.x version of the API.
Perhaps I just need to be patient for the next release!
Thanks again!