The NX's success depends on 5 things.
1. The Releasing Time
The Wii U has not had the pleasant year of 2013 like the Wii had of 2006. The reason sales are still only around 10000000 is obviously because the Wii U was released a year early. There were still underdevelopments in the console, so it did not sell well, selling less in 9 months the Xbox One sells in 6 weeks. So, they must make sure all parts of the NX are fully developed.
2. Good Battery Life
When the NX is released, people WILL expect good, hefty battery life. The Xbox One and PS4 had very good battery life. The Wii U Gamepad, on the other hand, opposed. Using the cradle and charger are better than using batteries though. And, the Pro Controller did have an awesome storage capacity of 80 hours charge from a charger. So, if the NX maintains that it will be another piece of the puzzle of success.
3. Imagination For The Games
Nintendo has been milking Mario for 31 years now. They need to start coming up with new characters. They can't keep having more Ubisoft games all the time, or Sega, or Capcom. They must come up with new characters, and make some more Mii-only games where you design your own world, control your own character and be whatever you want. And, if a game is popular the most obvious and likely thing for them to do is to invent a sequel.
4. No Extra Parents
They announced Flipnote 3D for the Nintendo 3DS to be launched soon in America but with no online ability for more parental controlling, even for ADULTS. A problem with Nintendo now is they are just way too overprotective with games these days. For the NX, Nintendo must let the parents parent and the gamers game. Yet they still must occasionally tell kids to take a break through their favourite character on the game.
5. Sustainability
Before Nintendo release the NX Console by atleast well into 2017, they have to ensure the console is so sturdy it is nearly impossible to break, as well as having an affordable price. There must be a very long lifetime on the console, being able to last for many years AND having a long few years' breathing space before hopefully the NEXT console comes out.
Thanks for reading, EmperorYT1.