Summary:
I would like to be able to left-click and drag on empty spaces in a panel, to move a maximised window that might be touching it.
This is similar to how you can simultaneously un-maximise and move a window in the Unity desktop.
See the following video for an example: https://i.imgur.com/OLw8Xll.mp4


How it can be implemented:
Perhaps a panel could check if a maximised window is touching it, and if it is the active window, clicking and dragging anywhere on that panels' empty space will un-maximise and move the window.

This feature should be off by default, but can appear as a toggle next to the "Floating Panel" toggle, when editing a panel using "Edit Mode".


Why Plasma benefits from this feature:
When a window is maximised and the user wants to move it, it is common to just left-click and hold the titlebar, then move the cursor to move it somewhere.

Using KDE Plasma, many people prefer to use a slim top panel, paired with an auto-hiding panel somewhere that contains application shortcuts and icons for open applications.

This isn't the case if one has configured Plasma to automatically hide titlebars when a window is maximised, to make the most out of the vertical screen real estate. It then requires clicking the "Restore" button using the window controls, or dragging another "grab-able" part of a window.
If one chooses to keep titlebars on windows with a "Unity-like" top-panel regardless, it still requires more precise clicking.

So with that in mind, this feature will help muscle memory a lot for anyone using aforementioned configuration, as well as being a quick alternative to moving windows with Meta+Left Click & Drag.

While it might be easy to just suggest "Well, if you want GNOME or Unity functionality, you might as well use those", but there are many KDE Plasma users of whom myself included, simply prefer the KDE ecosystem, a Qt desktop experience, both and/or more reasons to not switch away from KDE Plasma.

Thanks for reading!


SOFTWARE/OS VERSIONS
Linux: 6.3.4
KDE Plasma Version: 5.27.5
KDE Frameworks Version: 5.106.0
Qt Version: 5.15.9


Notes:
I believe this might have been a Latte dock feature at some point, but it doesn't work with the current version of Latte built from source and I believe it can benefit more users if it's implemented in the main Plasma panels.