We're told, though we haven't confirmed, that Canon will announce a 6K Cinema EOS camera to compete with the Sony CineAlta VENICE 6K camera likely in May of 2018 (though the announcement date isn't yet set in stone).
The new camera that could potentially be called the “C900” will incorporate a new full frame (larger than Super35) 6K image sensor.
It's possible the camera could be announced at NAB in April, but it appears more likely that it'll be announced after that trade show.
The same source also mentioned that Canon will be using their 8K camera that they showed at the CineExpo in 2015 for Japanese coverage of the winter Olympic games in PyeongChang, South Korea in February. The cameras will not yet be consumer products at that time.
More to come as we get further confirmation.