Europe could make more Azerbaijan situations work with the right language policies and enough time. By Azerbaijan, I mean a situation where there is an independent Azerbaijan, but ethnic Azerbaijanis across the border in Iran are satisfied with boundaries as they are.
The right combination of decentralization and language accommodations could lead to something similar to Europe's 3 tiered identities today. Its possible for an individual to have a concentric regional, national, and European identity. In modern Germany or Italy its possible to be a proud Bavarian or Sardinian, Italian or German patriots, and be a Europhile at the continental level.
The interwar Czechoslovak language law (schools, local government in your language if it's at least 20% of a local area) and some form of free-market arrangement that requires cooperation are important. Transylvania, for example, still has a somewhat distinct regional identity from the non-Habsburg parts of Poland. There's been mistrust in the past with the Hungarian minority, but separatist sentiment is only common among the over 60 crowd. Younger Hungarians grow up with their language in school, but most want to learn Romanian for economic and educational opportunities in other parts of the country.