[garbear]

Also since combos will bring problems sooner or later for differents configurations, I think we need an option to turn off/on combos.

The option to turn off combos is by removing them from joystick.xml. This will not be a setting in the GUI.

Anyone knows if xbox 360 guide button can be mapped? Context menu on that button could be nice.

Yes, the guide button can be mapped on all platforms. Not every controller has a guide button, so we might want more than one context menu button/combo.

What about when using an N64 controller? L + R + Start + C-Up maybe?. N64 has no select/back button. There may be others, but that's the first to come to mind.

I think this is based on 360 controller or any other actual controller that looks pretty much the same. There is no way to have combos on other controllers. Some has only 3 or 4 buttons. Or even 1.

Have you seen joystick.xml? Notice how the button names are for a 360 controller.

Kodi's input system knows how to map every kind of controller to every other kind (see how). No matter what is plugged in, Kodi knows how it maps to a 360 controller. This means that combos in joystick.xml apply to all controllers, assuming the controller has a button that maps to the 360's button.