LAYER MANAGER
The Layer Manager organizes geometry for user convenience which it does well. However, SU is being used for a variety of different purposes by so many people/disciplines.
I feel Layer Manager redesign needs to be a primary target of SU 2018. It could alleviate a lot of frustration for many users and facilitate modeling efficiency.
My contention is that it needs to be far more flexible/configurable, with hooks in the API that will allow developers to do their thing.
So, trash the UI.
Use the Spreadsheet paradigm. The current fields/columns would would remain the same (and perhaps unconfigurable ?) so that templates and models from previous versions would remain in tact.
The UI would be user modifiable. New Columns could be added which could be assigned properties which could be sorted alphabetically, numerically, etc., for instance: a project phase assignment and I suspect many other useful category designations needed for different disciplines.
Column order would be changed by merely dragging column headings with the mouse. They could be assigned a background color. Perhaps styles could be assigned to columns which could be toggled on or off for specific layer(s).
Layers could have sublayers ( a sublayer "level" would be assigned as a "child" column with the ability to control the indentation of each child column by allowing the user to drag the sublayer column borders sideways).
Layers could be put into groups (for 4-d construction phasing, progressive disclosures, project phasing, assigning the background color of layers in the Layer Manager. Layer Groups could be used to override certain properties of the layers contained within them. Layer Groups (and layers) could be manually reordered by dragging the layer vertically
Layers could be locked.
There would be a SOLO MODE for layers. When toggled on to Solo Mode, all other layers would be temporarily hidden. This would facilitate editing of complex models and quickly verifying that geometry has been assigned to the proper layer.
I guess you could consider this suggestion to be a Data and Geometry Management system with a Layer Manager contained within in it.