A combination of what if and the alternate history challenge, find a way for the Austro-Hungarian Empire to survive and live up to the beginning (at the least) of the 21st century. For it to survive to meet the standards for this what if, it must at least retain Austria, Hungary, and Czechoslovakia, bonus points if they still can have a small coast line (possibly retain Slovenia and Croatia)
Then, explain what sort of differences might occur in the timeline, and what influences a surviving Austro-Hungarian Empire could have on the rest of the 20th century.
The POD can be a CP victory, the Allies not forcing the Empire to break apart, or whatever you think will work to keep it around.