Total Commander

I think it would be great if root folder (C:\, D:\) has parent folder containing list of disks + My Documents and similar. The same what user sees when opening My Computer in Explorer.

I think it is logical that one can navigate throughout all the computer in the same frame without switching disks back and forth.

That feature is already available in TC.
Enter the following in wincmd.ini:

ShowParentDirInRoot=1

you can also set this via the configuration dialog:
Options > Display > 'Show parent dir also in root of drive'

Another possibility to access 'My Computer' is the TC command 'cm_OpenDrives' that can be used with a button/alias/hotkey.