I don't think that all typographical questions should be closed or migrated altogether. Learning a foreign language more or less includes learning how to align letters and symbols beautifully, how to choose appropriate fonts, etc., in that language.
And I doubt one can typeset a beautiful Japanese book without the deep understanding of the Japanese language. I've seen how many professional, non-Japanese designers can easily produce ugly design works containing Japanese, even to the eyes of average Japanese people.
I agree that technical questions about fonts should be migrated, but if the question is purely about the aesthetic aspect regarding Japanese fonts/typography, I think there is a room for allowing it here in JLSE. I'm one of the people who frequently post answers to typographical questions, and I'm doing so in the hope that it has something to do with helping average Japanese learners, not designers.
Note I'm not saying every typographical questions should be allowed, either — we need a consensus on each subtopic, particularly on how to treat font identification questions. While Graphic Design SE allows font identification questions, I can say for sure that they will be greatly bothered if all the font identification questions from languages all over the world are accumulated there.