Some suggestions for improvement of interaction with C4D interface :

Mouse icon color for warning

Use intuitively colored mouse cursor for warning against potentially destructive actions of some tools :

Problem : currently it often happens that selection tool selects invisible components, operations are performed on those components, while user is unaware. He might realize only after several hours of work, that his model was messed up. Same applies to cut tools, and paint tool. User should get clear warning that tool operates in a mode, that affects invisible components. The simplest way to warn user is to color tool icon displayed near mouse cursor on red. On the other hand, when tool is set to affect only selected components, mouse arrow could turn in green (green because it is rather safe : user has to select components first). Green arrow would help to avoid situations when let say cut operations are performed, but nothing is cut, because Knife was in "only selected" mode, while user cut through unselected polygons, thinking that the tool is in "all" mode.

Toggle commands for switching Visible/Selected states :

There should be toggle commands allowing to switch from keyboard between Visible Only / All and Selected Only / All states for all tools using such parameters. Now there is only the toggle for Visible Only / All, but it affects only Selection Tools, and not Cut or Paint Tools.

Display Tolerance Radius for Optimize Tool

Problem : Now, it is often difficult to properly define the tolerance radius for Optimize Tool, as there is no visual feedback. Often I had my models damaged, because Optimize Tool has welded points that should not be welded, and I haven't noticed it before it was too late (for undo). (eg. points have been at the opposite side of the object )

Solution : There should be an option in Optimize Tool, allowing to highlight points that will be merged, then user could apply the tool while in wireframe mode, and have a better awarenes what will be merged. Two colors could be used - one for points that will disappear in the process, second one for target points.

C4D could also provide a second option displaying the tolerance radius around points - radius could be displayed around only selected points, or if no selection, around the few closet points. (probably it should be not displayed around all points (it could slow down Viewport for very high poly objects)

Features mentioned above could also work for edges and polygons by highlighting edges or polygons that will be removed.

Adapt interface for UHD screens

Problem : C4D interface is adapted to HD screens, but on UHD (4K) screens most of interface elements are too small.

Solution :
- allow display of thicker wireframe (now only selected wireframe can be more than 1 pixel thick)
- allow thicker tools gadgets (e.g. axis)
- allow display of icons in 64x64 (now the largest size is 32x32 despite icons are designed in 64x64)
- allow larger icons in Objects Manager
- allow larger interface elements (files resource\modules\c4dplugin\schemes\Dark\normal.tif etc...)
- allow larger mouse pointer icons :

Slider color

Problem : now it is impossible to change the color of the slider - it is always gray

Axis mode :

Problem : Now it is hard to figure out that axis mode is active - the only difference in viewport is a tiny gray cube at axis center, which is often invisible, as it blends with background. We need better feedback, because currently it causes a lot of mistakes.

Solution : User awareness of Axis mode active could be easily improved by making axis much thicker in axis mode :

Other possible solutions :
- make central cube larger and blinking
- display axis icon with mouse cursor
- make axis icon (on toolbar) blinking in red while in axis mode.

Polygons highlight :

Problem : when linear workflow is used polygons highlight color is too dim . e.g. I define it as 100% green, but on viewport it looks like dim, dark green and its shade is influenced by the color of back-facing polygons (this should not happen)

Solution : Ensure that highlight color is closer to what is defined and not affected by backfacing polygons color.
Maybe we could have 2 intensities of highlight (full intensity - bright, fully saturated when modeling, and less intensive when user selects polygons for texturing and needs to better see the textures - there should be a command switching between those two highlight modes)