I set up multiseat with 2 AMD GPUs and 2 seats. Whereas seat0 uses Wayland, the other seat always uses Xorg. I looked into the gdm source code (for instance gdm-local-display-factory.c:create_display()), and it seems like Wayland usage is limited to “seat0” only.
Is this by intention? Is there some limitation in Wayland so it can not be used on more than one seat?