The new Blackmagic Video Assist 4K was introduced at NAB2016 this year and is now available. Quite a lot of features for the money: UHD 4K recording, SDI and HDMI inputs and outputs, Mini XLR audio, ProRes Proxy, LT, Standard and HQ recording, Canon LP-E6 batteries, a mental frame all with a 1080p touch display.
Watch this to see it on a GH4 and some early tests. This is the first video and covers some of the basic operation. There will be more that cover cards and audio.
The Blackmagic Video Assist 4K can be ordered through Adorama for $895.00
Shot with the Video Assist and GH4: