The physical discs and cartridges for the Wii U and 3DS, respectively, will not be backwards compatible with the upcoming console from Nintendo.
The news comes via Famitsu (and a rough translation), saying:
Since the Nintendo Switch is not a Wii U or Nintendo 3DS successor machine, you can not play with Wii U disk software and Nintendo 3DS card.
So, because the console is not a successor, you won’t be able to use the physical games, and that makes sense. The fact that GameCube games were compatible with the Wii was odd, and they were both disc drives, so it’s not something people should feel outraged over. Nintendo is trying to usher in a new era for their devices. The Switch itself may not be the best console, it may be amazing, but either way, it does seem like a good catalyst for change in the Nintendo platform.
The only other thing they had to say was regarding battery life of the handheld, saying you could, “play as much as possible comfortably even without a power source”
We will just have to see what Nintendo does next year, because there won’t be any more details this year.