I feel the problem with X is not the appeal, but rather Nintendo's lack of experience in marketing to the demographic it would appeal to. We're not talking about just general audiences or kids here. This is the sort of title which I view as a "big core title". Being a RPG is less important in this case than being a blockbuster. But the problem is, with these games you need very aggressive marketing to let that audience know that its a big deal. There's so much competition in this space that if you don't make it seem like a huge deal, you lose out to titles which do - including western titles like CoD, GTA, etc these days.
The sort of audience the game would be competing for are those who are used to seeing 8 page Famitsu articles with advertising spreads, lots of trailers and marketing in stores and all over. Having a big presence at game shows and events, and so on. Nintendo doesn't do that. In fact, they actively resist that style of marketing because they feel that their games can stand on their own quality. It's good to be confident about your product, but ignoring the business reality is part of what landed the WiiU in the situation it is today, and I fear that even if Monolithsoft gives their all on X, they will be let down by how Nintendo fails to understand how to engage the audience the game is made for.
I also don't feel that X is specifically a "Japanese" title. It definitely has international appeal, but again, all the points I raised apply to promotion in the US and in Europe as well.