A colleague just brought to my attention how annoying the display in Layout View is for the Legend. While in the actual legend itself you have the ability to use the group layer names for display, the list of legend items in the Contents pane is just a big old mess. Seems like potential UI fix to improve the legend display in the Contents pane to allow for groups as you do in the Map view. This would really help with organization for folks who have fairly complicated maps.
