Apart from linguistics (which I don't want to go into), there's not much to discuss about that, imo. Through urbanisation and the development of civic society, cultural differences across the empire would gradually fade, leaving behind mere shallow flavours as distinction. Ofcourse, this dilution of cultures would also be accompanied by a mixing of customs and values (also thanks to urbanisation and integral migration) of the different parts of the Monarchy, which would allow the development unique societal/cultural bonds tying the nations of Danubia together. This process was already well underway even IOTL.
I do believe that the labour movement and social-democratic values would be the things that would eventually mend the schism between Bohemian Czechs and Bohemian Germans. Then with Austria Proper remaining a bastion of liberals and conservatives, the desire of a unified Bohemian Crownlands separate from Austria could develop among the general Bohemian population regardless of language.
The strengthening of the left would have profound effects in Hungary as well. The ruling elite would initialise a policy of appeasement towards the minorities of the country. Keeping the socialists out of power would take priority over continued magyarisation (which already proved to be a failure in the countryside). This would work for a decade or two, but once the minorities realise the weight of their votes, they would start siding with the highest bider. The incorporation of Bosnia into Croatia, the Croatian separation from Hungary and the establishment of Transylvanian autonomy would all be the product of the political battles resulting from these developments. Like this, Hungary would gradually develop a bipartisan system with strong third party elements (kinda like the UK, now that I think about it).
The developments in Galicia would be somewhat similar to Hungary, or I don't know. I haven't really thought about it.
That's true, I suppose, albeit the bust of the 1870s could be said to be something similar. Still, a Great Depression-analogue of TTL however can not only show the weaknesses of the Austro-Hungarian system, but it could also increase the desire and will for reform. Such event could become the catalyst that sets Austria-Hungary on the road of federalisation, for example through the empowerment of the Austro-Hungarian delegation council and the common Ministry of Finance.