How powerful will Nintendo's next handheld be?

[Soundwave]

It will be powerful enough to port Wii U games/port Wii U engines to IMO.

This way Nintendo's dev teams don't have to make a big adjustment in development changes and Nintendo can port games like Xenoblade, Bayo 2, Captain Toad, DKC: Tropical Freeze, etc. etc. that a lot of people aren't going to get to play this gen because they refuse to buy a Wii U (don't think for a second Nintendo is just going to be OK with these higher budget HD games selling sub-1 million, sometimes sub-500k numbers). 

So quite powerful. You'll be able to play the same games at home (Fusion concept), just at 1080p + 60 fps and maybe some other added graphical effects.

The Tegra K1 is already supposedly as powerful as a PS3/360, even if Nvidia is blowing some smoke, by 2015, the K1 successor will match/exceed the PS3/360 level graphics, assuming Nintendo is not launching until 2016, that's another year for that level tech to scale down comfortably in cost for a $200-ish tablet like device with a 6.5-7 inch screen that isn't super high resolution (this is where Nintendo will save some money by going with a cheaper 1280x720 screen IMO).