I think one advantage in the future are the shrinking graphical jumps.Basically Nintendo needs to release an extremely cheap system next time that is very profitable from the get go. Because the other two options are releasing an expensive console that will just get them killed by Sony and MS, or they could take a loss which it seems is the biggest cause of their problems the last few years. Of course this is completely Nintendo's fault for going for that energy efficient nonsense. The Wii U could have easily been profitable at launch.
So they need to invest less money to achieve good graphics and to be closer in "psychological value" to their competitors.
At some point, as I already mentioned, it's going to be more important who offers the best services, exclusive games, the best idea, etc.
The thing is, we don't know how good it sells.Question: Do you think it would be worth it to create another system even if it only sold 10-15 million units assuming it was profitable to begin with?
What if they can sell 40.000.000 units next time.
The only thing that Nintendo can do is producing high quality software so that people have to come back and buy their hardware if they want to play those games, that's how they sustain as a company in long-terms. Every hardware generation is different.
And they certainly have to enhance other things like the overall console / multi-media experience (I think the Wii U offers quite a good amount of services, while it has it's flaws of course).