Austria still exists it's just a political and economic satellite of Germany.
Keep in mind that the Empire's Slavs were politically divided anyway, and a political alliance of the Austrian Half's Slovenes and Croats was a recent development late in the war.
What are you talking about they were allied both on internal front and external in the form the South Slavic committee.
From where do you think the State of SHS and later first Yugoslavia came from.
"Virtual independence" is quite literally the status of Hungary after 1867,
No it Wasn't,it was only becoming a significant problem post 1910. just before the War the trend would have undoubtedly continued.
You seem to misunderstand how Austro-Hungarian politics worked:
The House of Habsburg and the Imperial bureaucracy wanted absolute power and all the reform sin the the second half of 19th century came about because Monarchy was weakening and it needed to appease the national movements.
From 1848. to 1859. the monarchy was run under absolutism named after minister Bach.
That ended with the Habsburg defeats in the Italian wars. Several years after the Prussians defeated the Habsburgs causing a second crisis.
Habsburgs were forced to open up political life and create the Austro-Hungarian Settlement in 1867., which split the Monarchy into a German and Hungarian halves.
Slovenes,Serbs and Croats have Been in coalitions since 1880-is with varying configurations.
Do you know that Croatia was under Martial law just before the outbreak of the war?
Did you know that anti German and anti Hungarian sentiment was widespread in Croatia before the war?
Did you know many Slovene, Croat and Serbian POWs on the Eastern Front (Galicia) volunteered to fight with Entente on the Southeastern/Balkan Front?
In conclusion I think you based your plot lines on a superficial knowledge of Austro-Hungarian politics in the second half of 19th and early 20th centuries.
I have an Undergraduate Degree in History on FFRI, Rijeka, Croatia currently working on the graduate thesis.
There were several courses which dealt with history of Croatia under the Austro-Hungaria and one optional course which delt with the history of Habsburg Monarchy specifically.
Just so you know I'm not making this up.
That being said:
1.They could have taught me wrongly-unlikely
2.My interpretation is wrong-possible
3.Your interpretation is wrong-possible
Based on the above do you think Austria-Hungary would willingly grant concession that they usually just granted because of weakness or would they go nope, we are strong now time for another Crackdown, because it is far more important to appeal to German and Hungarian nationalists then the Slaves?
How do you think Southslav and Czechoslovakian soldiers and politicians would react to this?
Than you have two remaining problem the Croats and Czechoslovakian movement.
Croatians are weak and they may be repressed and apeased with some minor concessions.
How do we handle the Czechs/Bohemia?
Slovakia belongs to Hungary and they are opposed to even a notion of Slovakian autonomy.
Bohemia can never be incorporated in the German nation so let's just give them limited statehood in order to detach them from other Slavs.
Regarding the German and Japaneses realignment:
1.Germany having the manpower and Ships to occupy Indochina is laughable given their commitments in Europe and Africa
2.How do we address the Elephant in the room of Japan not going after China?
Possibble solution have Germany and Japanese agree to a division of interest spheres:
Japan gets Eastern Siberia, Pacific and Southeast Asia, while Germany gets China.
IJN faction prevails in Japaneses politics and the goal is to create a global maritime empire on the British model, which meant control of China to puppets and dependents rather than direct annexation. In my opinion is the only path to avoid Japan doubling down on it's OTL behavior.
The focus would than be to defeat Entente remnants and Russia and prevent Internationale fro gaining a foothold in the Japaneses Sphere.