Austria-Hungry spent so centuries meddling in the Holy Roman Empire that it never looked inwards at the cultural and ethnic divisions within. By 1918 Divine Right wasn't enough to hold back the changes made by the grievous loss of life and the sweeping Nationalism.
Maybe with a POD back during the War of Austria Succession, where Austria permanently loses control of the HRE, and decides that they are going withdraw Austria from the Empire to make their own bigger cooler clubhouse. Then spend the next three hundred years unifying their lands both culturally and linguistical, Slowly creating an Austrian Nation that has its own language(German with a Slavic flavor/loan words) and customs. While it would be completely ASB for all of the Austrian Empire to become united culturally, The Hungarians would never stand for it, its not too outrageous for a cultural melding between Austria, Bohemia, Carinthia(Slovenia) and perhaps Croatia.
Eventually Nationalism or some dumb war would have torn the empire apart but the division might not have been so severe