The war of the Spanish Secession or Seven Year's war are also considered as "world wars" yet they do not carry the WWnumeral name. Heck with all the nations fighting the War on Terror, should we name that WWIII? I just don't think we should get ahead of ourselves and naming this theoretical war WWIII as we cannot know with certitude how it will play out. That is why war's are usually named once they have concluded.