Create a new group layer property that can make it a "toggle group", only allowing one of its layers to be checked at a time.
Very often I want some of my layer groups to only display one of its layers at a time. For example, a group of aerial imagery coverages from different years. I rarely (never?) want two different years to draw at the same time because one will draw over the other.
It would be a really handy efficiency improvement if I could go into the group properties and check a box that makes the group a "toggle group" which would only allow one single layer to be checked on at any given time, automatically un-checking other layers in the group. I believe this would save time and image rendering resources, especially for workflows that require frequent comparison of different high-resolution imagery. But it could also be useful for comparing layers depicting different vintages of property ownership, jurisdictional boundaries, etc. 
Beginning at version 3.2, an ArcGIS Pro group layer has a Group Type property that allows sublayers to either be treated as checkboxes or radio buttons.
