The accepted idea of a World War 3 is actually in the second sentence of the full version of that beautiful wikipedia article you refer to. A conflict between Russia and her allies and the United States and it's allies using conventional military tactics and resources. The bolded statement seems very hypothetical to me.
If you were to say the war on terrorism is indeed a war, there has to be some victory condition for either side. To wipe out not a country, but a belief is impossible...therefore how can the war be won?