[tynorf]

Unfortunately:

  E183: User defined commands must start with an uppercase letter

[jessant]

command W <nop>

cabbrev w <c-r>=(getcmdtype()==':' && getcmdpos()==1 ? 'W' : 'w')<CR>

cabbrev q <c-r>=(getcmdtype()==':' && getcmdpos()==1 ? 'W' : 'q')<CR>

cabbrev q! <c-r>=(getcmdtype()==':' && getcmdpos()==1 ? 'W' : 'q!')<CR>

cabbrev wq <c-r>=(getcmdtype()==':' && getcmdpos()==1 ? 'W' : 'wq')<CR>