well, if the exploit is fixed in the japanese version, it'll be fixed in the US version, so there will be no reason to wait any longer since it won't work anyway.
if the exploit isn't fixed in the japanese version, and he releases it, it will probably be fixed when the english version gets released.
In which case, in the meantime he can poke around in the japanese firmware and see if he can find any other exploits. if he finds any, he can comfortably release ssspwn and sit on the additional exploits so that even if they patch ssspwn in the meantime, he'll have something else to work with and have a new entry point ready by the western release.
If it's not fixed in the japanese version, and he can't find any other exploits, then we're in a bit of a pickle, since releasing the exploit will almost certainly see it fixed in the western release, leaving us with nothing.