Have no fear. Nippon is actually the preferred official name of the real world nation (well nippon-koku). There's no way we could appeal to a Japanese market if we went with that name.
@Niedfaru @Giladis and @ anyone else who might make a decision about this someday:
If T9A ever does do an official Japanese-inspired army, I beg and plead that it not be called Nippon. Nippon is an actual, if archaic, name for Japan. Like calling the Knights of Equitaine "Franks" or something. For one, it would be really cheap. For another, to do so would undermine all the work T9A does to be thoughtful about culture, ethnocentricity and imperialism. Calling an army Nippon would basically say that Equitaine, Sonnstahl and Japan are all parodies of the real world.
In fact, one of the first things I did when I joined the team was attack the WIP names of every nation we had for being too much like real world counterparts. As you can see, the others changed, and I'll be damned if I'll let this one be the exception.
Prophet of Pavements