Like... parallel societies? Separate school, health, monetary systems? That looks like a brewing conflict once there's a conflict in meatspace that can't be solved in such style.
We don't need to eliminate states. We need to bring down remaining empires masquerading as nation states. Russia shall be divided by separating it's ethnic autonomies, Kaliningrad taken away, Crimea given back to Ukraine. Catalonia and Scotland shall be finally granted independence. Bavarian voices are rather silent nowadays, but why not.
Maybe if we eliminate states and administrative regions in favour of municipalities only (almost flat hierarchy with just two levels of government: municipality level and EU level), the localized "ethnic" tribes would be a lot weaker.