Anyone who says anything but the CORE MARKET either believe there is another gimmick like the wii which Nintendo can exploit (there might be!), or they haven't been paying attention to the industry at all.
Thier core fans?
Nintendo's dearest fans will always be around. Whether that default 15m pick up the system is entirely dependant on software, so write them out the question in terms of ''targets''. Just deliver Zelda, Mario and Smash in timely fashion and you've got them sorted.
Kids?
Most young kids pick up whats popular (PS1/PS2/wii/PS3/360) all of whom had success with young audience, so a console should never be tailored to them specifically (pretty sure more kids want a PS4 then a Wii U), they will come naturally when the price is right (for the parents), they are not early adopters so are also kinda irrelevant. In the meantime they will probably play their 360s. If we're talking extremely young (under 8s), I don't think thats a realistic market at all and the parents are probably more interesting in letting them play with their tablet as opposed to a 300 dedicated console.
The easiest and most obvious avenue for growth is the core market. That would involve cutting edge or at least modern specs (something Nintendo done without problem or a loss for almost 2 decades), rebranding (NES/SNES/n64 era) to move away from 'wii' or any other childish/casual connotations and Nintendo delivering their powerful first party games out the gate (hopefully some mature ones too-think N64), whilst fostering 3rd party relations along the way.
People really underestimate the amount of people who have been exposed and have appreciations for Nintendo's properties, anecdotedly all of my friends love Smash, Mario kart and the rest. Not one of them has a Wii U, nor do they intend on getting one. The world isn't split into fanboys, there are lots of reasonable people in between but without the recognisable and celebrated 3rd party games which dominate the industry and talking points each year, Nintendo are denying themselves a sizable audience. Most people buy 1 console per gen (unless a unique+cheap experiences arises like the wii) If a console doesn't have the games everyone is talking about, it not even going to up for consideration. Going head to head with Sony would probably be difficult but you don't need to outsell competition to be successful. Furthermore Nintendo have the opportunity to be at least 1 year ahead of the competition (the benefit the PS1 and 360 had).
Us core console gamers would jump at a system in 2017 that was future proof (within the next gen power bracket), running current gen games of the time, lets say Elderscrolls 6/GTA 6/Final Fantasy XVI/Stars Battlefront 4 on highest graphical settings at 1080p, 30fps versus the PS4/X1 running it at low, 900p, unstable 30fps. If the same console was bolstering titles like Mario Galaxy 3 and Smash Bros in its first year that would equal a win. The COD audience might be reluctant but we're not talking about replicating PS2 sales or even beating the PS5, simply looking at ways for Nintendo to grow from where they are now.
