Canon introduced the worlds 4K DSLR, something I was caught completely off guard with. Before hearing this news I was actually playing with a Red Scarlet and contemplating if I what my next investment to 4k would be. Canon introducing the 1D 4K had great timing for me because I was just looking into the 4K market.
The 1D 4K has a full frame sensor and can outputs video to 4096 X 2160-pixels (4k). To understand how big 4K is, here is a quick chart:
The advantages with going with Canon over other 4K camera, would definitely be the small form factors that made DSLR shooting popular in the first place. And the less accessories it takes to operate the camera.
The Cons would definitely be the lack of professionals features, like the XLR inputs, and advanced settings and frame rates. Although it might be to soon to tell what Canon will include in the 1D 4K.