Multiple keyboards with different layouts
It is possible to do this in the xorg config:
Section "InputClass"
Identifier "Keyboard Catch All"
MatchUSBID "058f:9410"
Option "XkbOptions" "caps:super,terminate:ctrl_alt_bksp"
EndSection
Section "InputClass"
Identifier "Apple Keyboards"
MatchUSBID "05ac:0236"
Option "XkbOptions" "altwin:swap_lalt_lwin,caps:super"
EndSection
However, GDM has its own way of managing you keyboard settings that will overwrite these xorg settings. I have not found a solution that works well with GDM.