Personally, I think that if World War 3 is to break out, it won't be a conventional war, and I'm not referring to the weapons used. Very likely, it's going to involve messy politics, rogue states, and terrorists. As for the weapons that will be used, I think that anything could be possible. Remember, there already are lasers that can shoot down planes. I think lightsabers-type weapons may already been invented by then, but I doubt that they will be used. Very likely, it's going to have nuclear bombs (or a derivative of some sort, such as a proton or hydrogen bomb), and biological weapons that can possibility change D.N.A. strands to actually "modify" the enemy biologically. Chemical weapons are possible, but I doubt that they will be used if there are such powerful weapons I mentioned above. "The force"-type weapons are also very possible, and we may be using them via a tool of some sort (I remember some Hong Kong science fiction movie predicting this). As for cloned soilders, it will likely be used, although such technology will probably only be utlilised by rogue states that have access to the technology.