Side note: Even if the leadership were True Believers (which I agree they aren't), Juche doesn't seem like the kind of ideology that could really be used to justify expansion. I understand it to be pretty ethnocentric. At most it would support unifying Korea. But I don't see it trying to expand outside "the homeland". You might see import substitution, less-open borders, restrictions on foreigners, stuff like that. If Korea had some grand historical claims I could see it going irredentist, but I don't think those claims exist.