At this point, I think Nintendo's relationship with third parties is key. This generation, third parties didn't develop for the Wii simply because they didn't want to, which broke a vital historical precedent in the console wars that the console with the most sales gets the most and best third party support. Without building a better relationship with third parties, Nintendo will be stuck in a no-win position: They'll lose, whether they decide to go toe to toe with the competitors with comparable hardware (see: GameCube) or do something completely different instead (see: Wii).
Aside from their third party relations, they need to produce a system with comparable graphical horsepower in relation to the competition, which also means 1080P support, now that HDTVs are commonplace. Thankfully, based on historical precedent, this coming generation will be more evolutionary than revolutionary in nature, which should make the process a bit easier. An overhaul of their online infrastructure will also be critical, as friend codes are far too unwieldy as is. They don't have to be a complete clone of the PS4 or the XBox 720, but they do have to make sure that they can accept cross-platform ports with great ease, which have become increasingly prevalent in the face of rising development costs. This would, at a minimum, give third parties experience in developing high caliber games on Nintendo's system, even if it isn't an exclusive, and get their feet wet.
Ultimately, it comes down to producing hardware that gets third parties into the door, and then making sure there's enough under the hood to keep them interested. There's no real reason Nintendo necessarily has to compromise on their vision of accessibility in so doing. I figure the third parties that have survived this disastrous generation (you know, record losses despite record revenue) would welcome Nintendo moving back toward the centre, and bringing their loyal core fanbase with them in that direction.
Personally, I think there's far more at stake for Nintendo in attracting third parties than may appear to be the case: If they go one more generation without third party support, it may permanently cement Nintendo's systems as perpetually devoid of third party support (like how few developers write software for Macs compared to PCs), and create a self-fulfilling prophecy that will be damn near impossible to break for generations to come: No third party support, which means no third party bothers to try, which means half-assed efforts, which means low sales for third party games, which means no third party support...
Super World Cup Fighter II: Championship 2010 Edition
