In college, I completed a paper that described the fighting between the Ustasha (ultra-nationalists), the Chetniks, and Tito's Partisans (communists) during WWII. I studied, briefly, the 20 years leading up WWI to 1945. With that, the thing I can recall as being the only option following the dissolution of the Austrian Empire was the formation of the Kingdom of Serbs, Croats, and Slovenes (KSCS) which took place in 1918.
Leading up to the assassination of Franz Ferdinand, the area in question was generally dominated politically by the Orthodox Serbs followed by the Catholic Croats who were in constant competition. Nonetheless, leading up to WWI, this area, with only a small portion of northern Serbia, was encapsulated by the Austro-Hungarian Empire. Many historians blame the outbreak of war on the Slavic-nationalists in the Balkans. More specific, Gavrilo Princip and the Black Hand a Serbian-national group.
With that being said, I find it hard to understand why they would eliminate the Austro-Hungarian Empire and replace it with a Serbian Empire per se. From what limited information and the the map that was posted by Огњен Шобајић, the "greater Serbian" state model would seem to eliminate the possibility of a representative or even potentially quasi-federal body that the KSCS had established. Rather, it suggests a politically and religiously dominated Serbian State which would be in conflict with areas like Bosnia and Herzegovina who were minorities in both aspects. If they were to use the greater-Serbian model, it would seem to hinder, rather than, help the Balkans. It would be interesting, if this was a real possibility, as to what this area might look like if they used the "alternative" option.
Unfortunately, there is not a ton of scholarship on the issue which makes topics like this relatively convoluted and difficult to discuss with often time alluding to speculation. That said, I did have to look a bit of information on wikipedia-- do not think less of me!
If anyone has more suggestion or better insight, please feel free to correct me. It has been a while since I discussed the topic.