I'm thinking that this could only happen if Charles I was able to successfully negotiate a separate peace with the Allies during WWI.
A peace that would have very likely involved Italy not getting all of its demands, and thus feeling extra-betrayed by their allies. If Italy gains Istria and Trieste, Fiume/Rijeka could remain Austrian. Additionally, I'd expect Croatia-proper and Dalmatia to remain in Austrian hands.
As far as Germany goes, if Austria pulls out of the war in the Spring of 1918, it is likely Germany wouldn't last enough to see a republican coup happen. Wilhelm II might be forced to abdicate in the subsequent peace, but Germany could remain a monarchy. That is not to say it won't go fascist at some point, just that it will be a different form of revanchist government than OTL's Nazis. Furthermore, Germany will also see the Hapsburgs in general, and Charles I specifically, as traitors to the German nation.
What happens in Russia with an earlier repatriation of the Czech and Slovak legions, without their need to go East, is another matter.
Whichever the case animosity between the Austrian Federation and Germany will run very high. Diplomatically, Austria will likely gravitate towards friendship with France.
Poland, Romania, and Greater Serbia (rather than Yugoslavia) would still be wary of Austria's movements.
A peace that would have very likely involved Italy not getting all of its demands, and thus feeling extra-betrayed by their allies. If Italy gains Istria and Trieste, Fiume/Rijeka could remain Austrian. Additionally, I'd expect Croatia-proper and Dalmatia to remain in Austrian hands.
As far as Germany goes, if Austria pulls out of the war in the Spring of 1918, it is likely Germany wouldn't last enough to see a republican coup happen. Wilhelm II might be forced to abdicate in the subsequent peace, but Germany could remain a monarchy. That is not to say it won't go fascist at some point, just that it will be a different form of revanchist government than OTL's Nazis. Furthermore, Germany will also see the Hapsburgs in general, and Charles I specifically, as traitors to the German nation.
What happens in Russia with an earlier repatriation of the Czech and Slovak legions, without their need to go East, is another matter.
Whichever the case animosity between the Austrian Federation and Germany will run very high. Diplomatically, Austria will likely gravitate towards friendship with France.
Poland, Romania, and Greater Serbia (rather than Yugoslavia) would still be wary of Austria's movements.