As of now there are not many consumer products, aside from a from a few smartphones (and the GoPro HERO3+ Black Edition), that can shoot 4k video. However the SD Association’s announcement of new Ultra High Speed Class 3 (U3) card labeling anticipates it becoming more common. The U3 designation guarantees a 30 MB/s constant minimum write speed, making it easier for buyers to know which cards are ‘4k ready.’
News: Digital Photography Review (dpreview.com)