No one sees how this as a problem? It can take a long time to set up a custom UI- many shortcuts, context menus and so much more. Saving it for future releases seems like one of the most obvious uses for saving at all.
How is it that Adobe After Effects doesn't even require you to load it in? It just looks for it, asks if you'd like to use the last version's UI and does it for you? Actually, that is the case with all the Adobe products, and they often have significant changes to capabilities and tools between major releases.
For the record, I rarely have had any problems importing old CUI profiles into Max. I think earlier this year I brought one in that was from Max 2020 to 2023 without any issues. Usually, I do it per module though: One for Color Scheme, one for Menus, one for Shortcuts, etc.
Doug Bowker
www.douglasbowker-motiongraphics.com