The main reason for the announcement is due to the mass of rumours coming out about the console all at one so in a way it seems to have forced Nintendo's hand, but at the same time other factors seem to have pointed in that direction namely the slowing Wii sales and the lack of any real substance to the Wii line up for the year beyond a handful of games.
I am going to take a stab in the dark at some things that I feel will be happening with this new system, first I feel full back wards compatibility with both Wii and Gamecube games, I also think it will adopt similar feature to what the 3DS has done and that is have much more in depth player profiles again using the Mii's as avatars and multiple ones on each system too for the first time, even doing away with the friend code system. I can also see it incorporating the Mii maker feature from the 3DS where you use a camera to create the Mii's likeness to your own, so I do think it will use that camera as part of the control too with maybe some enhanced version of the Wii-mote plus being used so it can be backwards compatible too, although I do think there will be some other additional form of controller too with an improved version on the classic controller pro with some sort of motion control in a similar vein to Sony's six-axis controller as well as rumble support but some other addition too to keep it fresh and unique.
Now what about the rumours doing the rounds? Well for one regarding power I can see it for one being easily able to match anything the X-Box 360 and PS3 can currently do and then some more, how much more? Well that all depends on how much it will cost Nintendo as they are not ones to build a console that will cost them money and they will also want to sell it at a reasonable price. As for the controller I have already said I think they will use an enhanced version of the Wii-mote plus that takes advantage of a camera to track over a sensor bar, but I actually think the classic controller pro will become the main form of control with all the extras I feel it will have that I stated above, and be a standalone rechargeable controller but the main rumour going about is it will have a built in screen now I can actually see this happening, but if it does or doesn't only time will tell.
What ever happens from now on out it really promises to be exciting time for Nintendo fans and gamers alike over the next few months and even year leading up to the release of the system.