Video preview? I thou the only way out for video is via wired hdmi?
The one we saw is hdmi -> wireless transmitter -> wireless reciever -> computer/monitor -> (Maybe iPad?)
But the camera still has to be wired to a 'large' transmitter which weights just as heavy as the dslr. If you are tripoding it, then it should be fine but still have to get a wireless transmitter that can accept batteries or make a diy ac battery pack.
U can use the dslr camera remote hd for the IPad to control your canon dslr. U can view , record and stop using the iPad in live view mode, need wifi to connect to dslr. Can adjust most of the settings. Simple to use and it's great software.