I concur,
'World War 1' or the 'Great War' if there was one, would be so alien to us that very little of the history of the 20thC would be repeated.
Without the Great War aviation development would have been far slower, the Communists would have probs never had there revolution without Tsar Nicolous making a massive blunder somewhere (unlikely). The 'Tank' would have never been developed and treaties like the Geneva Protocol would have never been signed. France and England woul not hae lost the 'flowers of their youth' nor have been bankrupted, and the US will most definiatly stay very isolationist.
What this means geopolitically?
The Colonial Empires of Britian and France would have retained much of their power into the early 20thC. Gandhis movement might never get up off the ground, and without the massive manpower losses of the Great War your going to see continued and greater industrialisation in Britian and France than there was historically.
While there will be more in Germany due to its greater wheat fields and heavy industry that developed as a later industrialisation process, your going to have all the 'high technology' of the world be primarially of British development.
Globally this will mean that with an isolationalist and 'anti-millitary' America Britian is going to retain and become stronger in her Great Power possition.
While not a superpower, it would be difficult for the continental powers of Europe rivial her, and between the three Great Powers your going to get a form of co-operative 'Cold War' where each is going to try to build the biggest penis on land, sea and air.
But without a major war lessons that were learned won't be.
By the mid-late 20s your still going to have infantry heavy armies, without the great artillery arsenels, machinguns will still be a fairly religated weapon, and mass stockpiles of chemical weapons will exsit, and these will be sat in a fairly passive-aggressive border post line.
Depending on how threatened the Entente powers feel towards the Kaiser of the given year you might get a detente forming into the late 20s to 30s if Germany does'nt pursue 'Großdeutschland' ideology.
This depends on Austria-Hungary's ability to keep the Slavic nation together. If the nation 'survives' to the late 20s, and the regining Kaiser is pro-Großdeutschland, then you might get a war between Austria-Hungary and Imperial Germany over Austria and the Sudenten lands.
Due to the industrial might, proximity and national sense. This war would be breif and over before it could ever develop into the trench warfare we have seen in our timeline. Hence Austria-Hungary would be forced to collaspe, and the Slavic states would fall into a civil war of self determiniation, that might not go well for the Hungarians and the Magyars.
This would be the kind of behaviour that might prevent a detente and might lead to the 'Great War' occuring in the mid 1930s. But I stress, only might.
Their is no reason to believe that we can actually predict a future without Princip succeeding, because it is such a pivotal moment in history. Europe was a specific tinderbox at the time, and any delay can change the course of events drastically.
The Short Answer: Nearly any possible history can result from Principe not succeeding.
