Total Commander

Sounds really complicated too me.
As pointed out earlier navigating between file panels on one side is done using Strg+Tab and Strg+Shift+Tab. There is no reason to change this. Just add a visiblity property to inactive tabs and add some layout options.

I think this more something that can be considered for TC 9.5.

Sob,
I'd argue for any of [1][2] to be "left" (whichever is active) and any of [3][4] to be right (again, whichever is active). There would be a shortcut to switch between the active (source) panels (so if the cursor is in [1] or [2] it switches between [1] and [2]) and another shortcut to switch the inactive (target) panel (so if the cursor is in [1] or [2] it switches the target between [3] and [4]).

While
[1][2]
[3][4]
might be useful I don't think it would work visually, there is no clear differentiation between what can be a target when the source is given. I agree it's less flexible without the "square" layout but I think it actually makes more sense the [1][2][3][4] way.

Roman