>>>     C-x w | split-window-right
>>> C-u C-x w | split-root-window-right
>>>     C-x w - split-window-below
>>> C-u C-x w - split-root-window-below
>>
>> These are really not easier to type than 'C-x 2' and 'C-x 3'. I'd rather
>> type simply 'C-u C-x 2' and 'C-u C-x 3' to split the root window.
>>
>
> But (1) C-u C-x 2 and C-u C-x 3 are already taken

You meant C-u is taken to split the window to exactly 4 lines high?

>>>     C-x w h window-height-adjust with + - = (repeatable)
>>>     C-x w w window-width-adjust with + - = (repeatable)
>>
>> These could be also repeatable with arrow keys, and one keymap 'C-x w r'
>> with mnemonic "resize".
>
> But then you lose the possibility to fit the window to the buffer
> vertically and horizontally (which is what the = key does in both cases),
> at least not without using some arbitrary keys for the two cases.  In
> practice I rarely adjust both the width and height of a window, but perhaps
> that's only me.

But then we could use two keys in the shared map, e.g. '|' and '-'.

>>>     C-x w m maximize-window-toggle C-u C-x w m minimize-window
>>
>> Window managers have shortcut keys 'x' for maximize, and 'n' for
>> minimize.
>
> Out of curiosity: which window managers?

On many window managers.  For example, this is how it looks
on MATE Desktop Environment: