About N4 the cars mustn't have always advantage, as well in IRC.
Maybe FIA want do the same for WTCC to attracting more private tuners team with japanese manuf. support. Just because there's 2 rounds will be held there. I think even for Mitsubishi or Subaru, both them had enough experiences to face road races, in the case they have cars in Super Taikyu(Japan's N4 track race series).