5) Arabs *read Egypt vs Usrael, the latter might count on the present economic weakness/crisis in Egypt and the absence of the Arab front against Usrael that could back up Egypt as in the past, mainly Syria, Iraq and Libya.. to launch some attack on Sinai and try to hod some terrain while invoking the terrorism threat, a fact which will provoke Egypt to a war where Usrael call upon the US to back it up, hence provoking a lot of alliances to be broken and new ones will emerge, since other Arab nations, most of whom are being on the US side will get involved and will side with Egypt.. Russia and China will see a golden opportunity to checkmate the Us in the middle east also and a semblance of WW3 might occur..
6) GCC vs Iran, while both have nothing to gain from a war, the Arabs do not like the Idea of Iran being present in 4 Arab capitals, be it Lebanon, Syria, Iraq and Yemen! An all out war will happen if internal conflict stirring is revived by both, since that is the main danger for them.. in that case the US will get involved in force to support its GCC allies, and Iran will count on Russia and China.. hence another possibility of a world wide conflict..
In brief, in any WW3 scenario, the common denominator will be the US vs Russia or China or both, while the trigger might be found in any of the 6 potential conflicts cited above..