I think there is a gigantic market for night trains in Europe. Now Eastern Europe never really moved away from the night train whereas western europe did. Central Europe held onto them longer than most and that is where we are seeing the rebirth of them. OBB has done a great service by providing night trains but it can't be the catch all end all of their development either.
What made Deutsche Bahn a really good operator is they are the country that is between western and eastern Europe and they are large enough that they can have more than one hub. München, Frankfurt, Köln, and Berlin are all natural hubs that all have a connection be it cultural, touristic, or business between the other large cities of Europe like Rome, Venice, Paris, Brussels, Warsaw, Budapest, among others. Germany had a good location for a hub and spoke network because it is in Central Europe which is essentially a gigantic crossroads. Which is also why most of the larger wars in human history like the 30 Years War occurred on German soil. Basically Germany is the equivalent of Chicago to the rail network of the USA. It's super big, and in the dead center of it all.
Austria is just a bit too far south to really play into the hub and spoke system so while it is great that OBB has saved the Night Train it's growth is relatively stunted because of it's location in Europe. Unless NightJet becomes an open access operator serving domestic markets and fifth freedom routes outside of Austria/Germany.
The biggest hub I see in Western Europe is Paris, with a very small more regional in nature hub in Barcelona.
In Central Europe Zürich stands out to me as somewhere that has a lot of growth potential. Somewhere I have made an interactive map of European night services. I should find that again. If I remember right Romania had a lot of trains.