Sorry but they really aren't. I don't know why people keep saying this. Assuming this whole 2 SKUs with a unified library thing is true then that would mean that all games would have to be created with assets that are at least acceptable on the stronger SKU, but also work on the weaker SKU, generally resources needed per game would rise and while there might be somewhat less long droughts Nintendo would surely not be able to adequately support the system on their own.
I think we kind of got an early taste of the future with Super Smash bros. with it launching on 3DS and then polished up graphically for the Wii-U. But i agree, just unifying the platforms is not enough. Handheld market is still shrinking so they would end up with an even smaller install base than they have now.