The terrain layers could be at the bottom of the layer list like in the default sceneviewer or inline and in groups would be useful to allow a group to be toggled on or off.
I am currently creating a viewer for a client to view multiple epochs of captured terrain data and they would like to be able to control which one is visble through the layer list
eg: At Bottom
x January 2021 Imagery
x January 2021 Features
o February 2021 Imagery
o February 2021 Features
o March 2021 Imagery
o March 2021 Features
x January 2021 Terrain
o February 2021 Terrain
o March 2021 Terrain
eg inline
x January 2021
o February 2021
o March 2021