There's a big thread in xbiz forums regarding 4k. Looks like there are a few shooting in it now.
Whether it's going to be needed in the next couple of years is beyond me. In reality, I understand wild life editing worthy in 4k, but the difference on a standard 42inch tv is probably so slight, maybe the standard hd shall be enough. Only time can tell
We're shooting in standard sd on the canon & panasonic, hd on the live cam & sony z, which actually do also capture in 4k, but with the obvious lens size, the quality isn't as intense as the panasonic tbh.