Some early specification of Panasonic GH 4K camera surfaced over the web, the camera seems to have very advance core specification for video users.
Take a look at the Panasonic GH 4K Camera rumored specification
1) It will have a quad core processor.
2) Sensor reading is 50% faster then GH3 so much less rolling shutter.
3) maximum bitrate of 200Mbps ALI and 100Mbps IPB
4) 4K, you will have MOV + MP4 only.
5) In 1080p you will also have AVCHD.
6) The camera will have focus peaking and the user will be able to change the color. Focus Peaking will also work from smartphone through wifi.
7) Focusing will be faster and have more AF points (compared to GH3).