I think UI is more like a food. its really up to individual preferences. some people like spicy food, some people even like to eat dogs? (joke) anyway, If we spend enough time on a software, any UI will feel comfortable. IMO, currently Rhino UI is more CAD-oriented, which is why everybody who is accustomed to drafting pick it up easily. by comparison, Zbrush UI for me is more like - Photoshop-oriented, so each software develop their own UI because they realize there are huge market targets.
I also use several other software and from what I can say, they always stick to their own UI concept since day 1, which means there is no way 3dsmax somehow adapted Maya’s interface, vice versa, because millions of user already accustomed to it. but I notice, each upgrade they tend to make it simpler, easier to understand for beginner, and more elegant design. (less is more)? some suggestion I can steal from other software includes=
Color Coded Icon (for instance, Mesh and NURBS command have different color for its icon, or certain command like dimension, hatching, etc can be in 1 color group.)
Context specific command (a command suggestion will pop up if we select certain object) for instance, if we select 2 intersecting curve a “split” or “intersection” command will be added to the “pop up” command
Autocomplete command with Icon displayed (just like grasshopper). new user sometimes doesnt know what “booleandifference” means. having the icon displayed alongside with the command text will help them.
but definitely having suggestion from other user from different software background can be interesting, especially (well this is selfish) BIM in revit.