The GH3 certainly does allow RAW shooting at 16MP in electronic shutter mode; I use it all the time.
Rolling shutter should be reduced with the GH4's e-shutter as the sensor read speed has been improved by 50%. It should also be useable with ISO 3200 whereas with the GH3 it's limited to ISO 1600.
I have read, however, that the GH4's e-shutter files will be 10 bit only, whereas the GH3 captures 12 bits with e-shutter.