If they add another axis army then definitively not the Japanese but a third German army, maybe the Oberkommando Süd. In that case we would have a German Army each for the East, the West and the South. The Southern Army could be built on the remnants of the Afrika Korps (some PzIII modifications, the mighty 88 flak gun, Marders, etc), the former Italian Army and the elite Fallschirmjäger troups (Monte Casino). Maybe that would work.
Out of all the bullshit being thrown around here, this is the most reasonable and down to earth appraoch.
Japan is so out of question, if you look at all the other armies and their respective commanders and abilities. Even though it's also bullshit that brits can fight okw on kholodny ferma alongside with soviets, a japanese faction is a totally different level. I would like you to think from Relic's perspective and look at their previous factions and their commanders, their general theme and their respective places in the game. Japan just does not fit in. I must admit it is very intriguing, but too far fetched.
I would also much rather have some Afrikakorps/Oberkommando Süd, mixed in with Italian units or call-ins. We are likely to get neither though, so we should be glad to get anything.