Nintendo's not ending up like Sega. Unlike Sega, Nintendo isn't burning itself and its funds out on multiple consoles in a short period and killing the trust of fans--which is a stupid idea some analysts have brought up (Nintendo should scrap Wii U and do a new console, it's like they never heard of Sega).
Also Nintendo is a gaming company. It can take risks and loses and keep going. It has the bank roll to do that for several more generations of consoles. It's a luxury that Sony and Microsoft don't have because they have their hands in several pots. While that would bring in money, they have areas that just aren't profitable. If a console begins to falter, they can always offset the costs, but that's not something they're going to want to do. It's why the PS4 can't fail or have a long period of slow sales.
A year of slow sales for Nintendo would be different compared to year of slow sales for Sony at this point. Sony and Microsoft have more in the bank and could do what Nintendo do in failing--if they were gaming companies only. Instead they wish to do entertainment, music, computers, smartphones, OS's, tablets, lawsuits against Google, other technology and so on.
A success because Sony did it twice in a row with the PSX and PS2 with outclassed hardware and Nintendo did it last generation with outclassed hardware. Honestly, Nintendo looked at Sony the prior two generations and did what they did, Sony decided "We have to out do Microsoft's next console" and ends up doing what Nintendo did in those two generations with stronger hardware minus the pricing.
Which Nintendo did right with the Gamecube in even though they came in 3rd of 4, they were still profitable on hardware with better hardware but was trumped by PS2 in sales and they were profitable with the N64 and trumped by PSX in sales (that was down to having games that were equal to crack offered at high prices and high licensing fees).