Thank you for your palettes! They contain a huge commands and have a small size. Your palettes are convenient and helpful as opposed to standard Mathematica palettes.

Some of my thoughts on palettes: The principle maxim is: Maximize the functionality; minimize the space.

Since screen real estate is valuable there are a few things to be wary of. Don't use a lot of nonfunctional decoration on the palette, or expansive spacing. Don't use a huge billboard of symbols if you can avoid it. Don't use permanent space for something that is infrequently used. Minimize any changes to a user's Mathematica Palettes menu.

Over the years I have evolved a palette design that I feel is useful for moderate size applications with packages, or for convenient use of some related subset of Mathematica commands. It is not useful for Mathematica as a whole because there are just too many commands.

For these palettes I have chosen as the most useful information: 1) An overview of the routines available; 2) Links to the documentation for the application and individual routines; 3) Paste buttons providing labeled templates for each of the commands.

As an aside, palettes can be added to the Mathematica Palettes menu. If you follow the prescription for writing applications they can be put in the FrontEnd/Palettes folder of the application. If you have multiple palettes it is useful to add an extra folder with your application name and then put all the palettes in that folder. Then all your palettes will appear on the Mathematica menu under one entry, won't be scattered all over the user's Palettes menu and won't clutter it.

I have attached two palettes. One is a UnitsHelper Advanced Palette for a UnitsHelper application that I have to provide more convenient usage of Mathematica Units. There are also additional application routines and documentation which I am not providing here, but there is plenty enough to see how the palette works. And it does have access to all the Mathematica routines and documentation as well as relevant NIST pages on units. The second palette is for the Mathematica Geometry routines and should be fully functional. You could open these to explore with a Mathematica notebook.

There are three space-saving devices that I find most useful. 1) Openers to group various functionalities; 2) Dropdown ActionMenus containing groupings of functions and routines or containing a list of Help links for the routines; 3) Tooltips on the dropdown menus that give a compact list of the routines in the menu or ancillary information. Also, the palettes have the standard Size button on the frame so a user could make the palette smaller, according to how good his eyesight is, or only enlarge it when using it.

Most of these elements are present in the Basic Math Assistant palette although it is directed more to beginner or basic use of Mathematica. It does use a fair number of 'billboard displays' (Do we really need to punch in digits from the palette when they are already available at two places on most keyboards?) and only has direct help links to overall tutorials and not individual function pages. The palettes I'm showing are more appropriate for a set of several hundred commands from an application or as a related subset of Mathematica.

The following describes the UnitsHelper Advanced Palette.

The top button is a dropdown menu to directly load the application or paste the load statement (much the better choice). The second, Documentation, button gives access to the UnitsHelper documentation (not available here) and the WRI guide and tutorial pages. It also gives links to various NIST pages.

The Units and Prefixes section gives the various System, Prefixes and units organized into groups. The SIPrefixes for example gives a list of the standard prefixes annotated with their numerical values. For each of the dimensional unit groupings two dropdown menus are provided, the first ordering the units by magnitude and the second alphabetically. The items, of course, paste the unit into the notebook.

The Physical Constants sections just gives the constants alphabetically.

Skipping to the Wolfram Units Routines we see the method used for displaying routines. The "?" dropdown gives links to the Help pages for each of the routines. The group heading has a tooltip giving a compact list of the routines in that group, When the dropdown menu is opened paste buttons are provided for each of the routines. A button is generally provided for each overloaded version of the routine.

The second palette, Geometry Palette, for the Mathematica Geometry routines, can be explored for yourself.

Attachments:

I don't like the ribbon itself, but I thought that the developers can place the packages menu in its own tab in one ribbon, so that will be convenience.

You can create ribbon toolbar based on DockedCells and TabView and other ui elements.

Then you can move Default.nb to appropriate place in $UserBaseDirectory and make this DockedCell a default one. See General approach to modifying built in stylesheets to get an idea.

If you want to add new items in menu bar / Edit or anywhere, copy MenuSetup.tr to analogous dir in $UserBaseDirectory and edit it accordingly. See this topic https://mathematica.stackexchange.com/a/109396/5478 where I created an additional menu to quickly open important directories.

I'm not 100% this answers your question so sorry if I missed the point.

p.s. about stagnation in GUI updates, yes, we are victims of a need to keep things consistent across Mac/Win/Linux and now also web FrontEnd as well as iOS.

Thanks for reminding me why I stopped using MS apps. My comments are in response to the Apple apps and some of the word processing apps I use on macs. Not everything that they do is applicable to what is needed in Mathematica, but, for example, moving some of the functionality present in the Writing Assistant palette to the Formatting (Edit) bar that can be optional shown at the top of a notebook window would be useful.

The UI in general in Mathematica is improved with each release. The palettes seem to be stuck in version 7, though. It may be a case of "if it's not broken, don't fix it", but there are some refinements that can be made.

The main problem I have with palettes is on my small laptop, where it can be difficult to manage the screen real estate, especially if I need to make the notebook window wide to accommodate some nifty graphics, or a multi-column table. It is in these cases where I may have to constantly move a palette or even close it to see that I need to see in the notebook. This is not an issue on my iMac, of course.

To the contrary, I utterly hate and detest the ribbon toolbars in MS apps.

Palettes in Mathematica can stay where you put them. I love the decoupling between the separate palettes and the main work areas, namely, the notebook windows. to say that positioning them takes more time than using them is utterly absurd.

The "interface", contrary to what you claim, is much more friendly with practically each new release. For example, the pop-ups for possible autocompletion, with quick links to help or templates to paste, are very helpful, for beginners and experienced users alike.