Comment 18 for bug 313514

Two ideas, how to accept keycodes > 255 it backward compatible. All of them are ugly hacks, but may be accepted in X11 line:

1) evdev driver will query kernel for all available keys on all configured keyboards, then it will create table of false one-byte keysyms. In correspondence to them it will also write temporary xkb keycodes/evdev table.

2) X will accept keycodes > 255 internally, but in protocol level it will provide correct keysym with possibly incorrect keycode.

For both ugly hack is valid following limitation: Most applications read only keysym, the rest will break.