Allow Mixed Spatial References in WAB Basemap Gallery Widget

[mpboyle]

I think it would be nice to have the base map gallery widget in Web AppBuilder (Dev edition 2.2 if what we're using) allow base maps that use more than 1 service the ability to mix spatial references.  Within ArcGIS Online, this doesn't seem to be an issue, but if we use the same web maps as base maps within the Basemap Gallery widget in Web AppBuilder, it doesn't seem to work.

We like to use the Esri Imagery (Web Mercator) service as a backdrop for many of our imagery base maps because it provides a continuous image.  On top of that, we would like to pull in historical imagery hosting by our State, but their image services are in UTM.  Again, within ArcGIS Online, this isn't an issue and works great, but if we try to use the same layering or the same web map as a base map in Web AppBuilder only the Esri Imagery service shows.

[JakubSisak]

I believe this is an essential feature and should be added to ArcGIS Enterprise Portal.  Not matter what we do we are unable to add ESRI basemaps to our gallery. Our data is in UTM and our scale levels are configured differently - it would be fantastic to be able to use ESRI basemaps and our own basemaps in the basemap gallery and allow users to flip between the 2.  As this isn't an issue in ArcGIS PRO nor ArcMap