John,
This is a situation where you may not necessarily be able to have your cake and eat it, too. It depends on how your are currently operating.
If you publish all of your map services in the UTM coordinate system, the coordinates reported will be in UTM. But that basically precludes you from using any of ESRI's basemaps. So, if you like and use ESRI's basemaps this may not be an option.
I have the other side of the issue--I publish everything in our State Plane coordinate system, including our own basemaps. My users want to see the "mouse-following" lat/long display but the coordinates are State Plane.
As a compromise, my users use Robert Scheitlin's Enhanced Draw and Measure widget to get at coordinates. The coordinate text persists, so it makes it easier for them to transfer that value rather than attempting to keep the mouse still enough so the value doesn't shift on them.
But now that the Flex Viewer is "dead", I am shifting over to HTML5 using the Geocortex Essentials product. It allows me to still use my AGS map services directly without resorting to AGOL or Portal and ESRI's overpriced named user model. I'm also exploring--a bit more than casually--the open source offerings on everything in the GIS stack because I see the day coming when ESRI forces us all into the named user model (with ArcGIS Pro) and prices us completely out of continuing to use ESRI products. And I'm fairly certain my organization isn't the only one that will be in this situation.
Brian
