Regarding the design, I think the ModernGUI approach makes the best use of the available space. (thanks for preserving this work from boonGUI @Atrik) IMHO adding a separate panel dedicated to these actions introduces a few complications. For example, if only a few actions are available, the panel would need to resize dynamically. Otherwise, it would leave a lot of empty space. This already happens when selecting buildings, where only three actions are available. On the other hand, if more than ten actions become available in the future, the panel would either have to grow or choose which buttons to display, just as the current vanilla implementation does.  In fact, this already happens when selecting units together with buildings. So I think some level of tolerance for certain buttons not being shown under specific conditions is necessary. Otherwise, we'd have to resize the bottom panel dynamically, and I don't think that's a desirable solution.

I think I'll consider this proposed layout, I see a some benefits. One of them might be an option to hide it as some players like myself already know each unit command hotkey. I also like that you get 10 slots for unit commands which is the exact number to not have any overflow for single-type selection even including new capture button (the 10th is "back to work") but doesn't have much dead space. The overflow in multi-type selection (worker + building) will overflow but that's somewhat fine, not worth adding space for this. About the construction panel layout, it's not worth pursuing your attempt to order building, in my opinion. Due to the fact that the list of construction is very variable : across civs, mods easily add some, and in a multi-type selection (if any of the selection is a trainer, a researcher or can be upgraded) then you cannot keep the ordering. Also on your mock the order isn't even done by any entity classes that would make it possible.

The button does work, but after clicking on it you need to left-click the terrain to issue the command, just like with the other command buttons in the panel. You can try the same with Patrol, Guard, Repair. When using the hotkey instead, the command is issued with a right-click.

Good!  

That would be a LOT of issues probably at least a thousand of the 1.6k issues we have