Well, Canon seems to be happy with their lens lineup for the 5Ds/5Dr, which are 50 MPX cameras and, off tests, there's some, albeit marginal, improvement over the 36 MPX Nikon D810. Pentax has a much lauded 645Z MF camera with 50 MPX, so everything is moving toward that 8K (33 MPX) mark.I think the problem now is lenses being good enough for 4K and 8K, and storage, and whatnot. I mean lenses now you can't really have them wide open on F1.4 or 2 if you want the resolution to be good. Maybe that's is less of problem on bigger sensors closer to 65mm...
Ikegami will be showing an 8K camera at the NAB. Within a couple of years, 8K should become high end pro accessible. On the consumer front, owners of high end front projectors will be interested. Anyone else probably won't.