A triangle is 2D. It would have to be a pyramid, cone, or triangular prism.

Getting back on topic on thing I would really like to see would be standard wireless controllers. Each controller should have a removable cord so that you can play it wireless or you can save batteries and plug it into the console. I would also like the controller to have a decent sized D-pad and the buttons aranged in a normal manner. The Cube controller design was great in theory and worked perfectly with Nintendo's own games but it was a nightmare for ports and most third parties didn't use it correctly. Something more generic would have more appeal. If they wanted they could make it so that Cube controllers can work on the new console as well and then have the best of both worlds.
I also would like to see a mouse (and maybe a keyboard too) released. That way they can make games like RTS games and point-and-click adventures. Plus you could have mouse aiming for first person shooters. They could then pack it in with a major release (not Mario Paint, an RTS would be less gimmicky) to ensure it gets a good sized userbase. The SNES mouse flopped but PC games are a LOT more popular now than they were ten years ago so the amount of games that could use such a device is much greater. Plus it's something the competition initially wouldn't have.