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I think the main audience honestly is kids (outside of the Japanese market).
They need kids, they can't just surrender an entire generation of kids to tablets, even if they are playing some Nintendo games on those tablets.
They need more of those kids to buy dedicated Nintendo hardware, NX will be a gaming tablet for that audience primarily.
Of course older Nintendo faithful will buy it too because they kinda have to in order to play future Nintendo games, the sales pitch the older gamers will basically be the same old "don't worry, it has Zelda for you".
If they can sell a tablet for under $300 that plays Nintendo games, maybe even comes with an Amiibo toy or two, and can also play the popular Android games that kids love ... Nintendo will probably be able to carve out a market in the West even.
It might not be as huge as they're used to in the past, but it's better than nothing.
I think they've mostly given up on trying to compete with Sony/MS in the West, and probably even that Wii casual audience, I think they understand the adult side of that is too content with their smartphones to buy a dedicated gaming device. But they're not willing to let the kids market go entirely tablet. If those kids love tablets, then Nintendo is gonna give them a Nintendo tablet, a pretty darn good one (for a mobile device) from the sounds of it.
