First off, i know this does count as multiple ideas but they're all tied together!
Rigging, skinning and animation are a huge part of this software, but the character creation process using max's stock capabilities is plainly speaking just bad.
The character animation toolkit and the max modifier stack are two of the best features max has in terms of character creation but they are held back by two of the worst features max has to offer, the skin modifier and the morpher modifier.
Custom rigs and FBX imported characters: Waste my time!
Creating and setting up rigs outside of cat can often be a pain in the polygon, allow us to convert maxbones or helper bones into cat rigs without rebuilding the whole rig from scratch and fiddling around with skin utilities or envelope exports wasting hours and hours of time.
Skin: Has nothing to do with realistic skin!
The current skin modifier is full of bugs and completely outdated the only remotely up-to date features are dual quaternion skinning and the voxel solver, people have complained about it 10 years ago, comparing it to solutions present in other 3d applications like maya or even plugins like BonesPro, DeltaMush the skin modifier lacks in alot of aspects.
-Give us the option to skin using a falloff value and vertex influence
-Add a option that allows the definition of areas for soft body effects like jiggles or fat and muscles similar to SkinFX.
-Implement solutions similar to bonespro's meta & parabones and skin collisions for accurate deformations that prevent clipping around thighs, knees and elbows (Implicit Skinning).
And last but not least...
Morpher: I can't read the target names because they're too long?
Improvements for the morpher modifier have been requested a couple of times
in it's current state the targets are hard to manage and sort.
A rework to the overwall modifier in terms of UI and visibility would do wonders, every morph target with a name longer than 12 characters gets part of it's name cut off, this can make it really time consuming and annoying during animation process when searching for the right targets.

-Expand the textfield when the Command Panel expanded
-Allow us to color Code Morph Channels
-Allow more than 100 morph channels even when loading them individually, currently the only way to load more than 100 is by using "Load Multiple Targets"
-Swap Morph Target Channels by Drag & Drop
-Better Vertex Selection Morphing and Mirror Morph Target
-Backup Morph Targets external -> Improves Autosave time with Scenes that have alot of Targets
-Add a Base Morph Target that stores the mesh in it's raw shape so that we'll be able to rollback after using "Capture current State"
Sadly the features max gets usually end up being fancy and new instead of actual improvements that the consumers wants implemented, viewport tearoff is a good example, it's been suggested years ago and still is not implemented even though it's the highest voted suggestion in the forums.
Thanks for reading this.