Vitaly, please take a look at this:

The big improvement GH2 can get in a next GH3 or GH4 model is enable a HDR function for video. Not the cartoon look HDR, but the improved latitude dynamic range HDR

The best solution would be to get two video streams from the same sensor at the same time, with same shutter speed for both, probably using different iso for adjacent pixels, half pixels at low iso, half pixels at high iso, and the camera merge the two streams into one video mts file. or to use same iso with a sensor designed to have half pixels in a small size and half pixels in biger size. Or to combine some pixels like the idea on the link below. This method would be very better than the Magic Lantern HDR solution for Canon cameras using two different exposures in different consecutive frames.

Please take a look at these solutions showed in these links so you can help Panasonic to develop a HDR video solution for M43 cameras.

http://finepix.com/exr_cmos/en/ (click in DR wide dynamic range in the middle of page, great sensor design)

http://www.fujifilmexr.com (skip intro and go to EXR modes explained / dynamic range)

http://en.wikipedia.org/wiki/Super_CCD (the versions of HDR sensors developed by fuji, nice sensors designs)

http://www.sony.net/SonyInfo/News/Press/201201/12-010E/index.html (scroll page down to see hdr video sensor concept)

Hope this can be done some day, it is the big step forward!!!