Sunday Night, April 6th, at 2PM Pacific, 5PM Eastern and 10PM London time, Sony will hold its annual NAB Press Event. The rumor sites are pretty much all reporting that the company will announce an "A7s" 4K full frame video/still camera.
Full frame is nice, but we'll have to see whether the new camera's codec and connectivity measure up to the GH4's.
Sadly, I don't get to Vegas until Monday night, but Sony will live stream the event - so we can all watch it right here on HCR!
EDIT: Okay, okay - it's the world's second full frame 4K camera (after the very expensive Canon 1D C). That said, it is likely to be the world's first full frame 4K camera that many people can afford.