Indeed, such exclusion is expressly forbidden by the IR.
Heh, never thought of such an application. Usually the IR was to protect against governments that wanted to prevent their nobles from attending to other realm's tournaments, I don't recall any case where a realm sponsoring a tournament tried to dissuade certain realms from attending. The IRs are overall personal rights, not collective rights, though being able to punish a collectivity for acts of its individuals, without that collectivity having the right to punish the culprit individuals, would lead to messy situations, I reckon.
