Problems to be Fixed by Canon:
Canon can tweak its software to rectify a few problems that we face.

12.Quickly shifting between Video and Stills:
You can customize the Mark IV so that when you press the FEL button the filming starts. However, one should realise that for still photography we use a high shutter speed to get images sharp. In case of videos, we need a low shutter speed. So when I shift from shooting stills to video I can quickly start filming by pressing the FEL button, however, the settings are carried over from stills. So I have to first reduce the shutter speed and then press FEL button for filming. It takes time.
Canon has made a provision that you can interrupt filming and shoot stills by pressing the shutter at any point of time. However, that means the still images will also be shot at low shutter speeds. That will result in still images not being sharp and unusable. If you are using a wide angle lens or an intermediate lens, then slower shutter speeds can be ok. However, if you are using a heavy 400mm f2.8 L IS lens with a 2x II Tc then you will realise that it becomes difficult to get sharp images at slower shutter speeds. It should be noted that the Canon 1D Mark IV requires higher shutter speeds than other cameras to get sharp images, primarily due to its higher resolution.

What canon can do: Canon can come out with a firmware upgrade so that when I press the shutter button, the shutter speed should be as defined while shooting stills previously.

13.Shifting video modes and use of 60fps at 1080p:
At present I shoot at 1080p at 24 frames per second to get the film look. The options to shoot 60frames per second is not there at 1080p. You can shoot 60 frames per second only at 720p.
Why do I need 60 frames per second? Imagine a bird in flight or some rapid action. At 24 frames per second the action won’t register properly. When you shoot at the higher 60 frames per second, the action will show up as slow motion and we would be able to appreciate the scene better.

Unfortunately, at this point in time, we can’t move from 24 to 60 frames per second at the click of a button. Further, 60 frames per second can only be shot at a lower resolution ie. at 720p.

Technically, 60 frames per second would place a bigger challenge on the Digic IV processor. Canon has to decide whether the current Digic IV processor is capable to do that or not. However, smoothly moving from 1080p Full HD to 720 p HD should not be a technical challenge. I think it is because, during the beta testing state, the Canon EOS 1D Mark IV camera may not have been used much by wildlife film makers.

What Canon can do: A firmware upgrade to enable one of the buttons to help shifting from 24fps to 60 fps on the fly.

14.Overheating:
The LCD at the back gets heated up after shooting for some time. Though I have shot in Ranthambhore at 40 deg plus temperatures, but I haven’t recorded at a stretch for 12 minutes. I haven’t experienced the Mark IV stopping due to overheating. However, I am not sure about the impact on the image quality. When the sensor gets heated up, the noise is bound to increase. Even shooting still images with prolonged live view usage is going to increase noise in your still images. And the person who is going to shoot both stills as well as filming, there is a possibility of getting noise which would be evident when you pixel peep your still images.

I will update this review as my understanding and experience continues to increase with the Mark IV.

Conclusion:
After reading this if you are getting a feel that Mark IV cannot be used for filming, then you are definitely wrong. I am just attempting to inform you all the pros and cons of this disruptive innovation introduced by Canon. It is certainly a game changer.

This is the best Canon camera till date.

The video is not just a function added to the camera. It is not only broadcast quality video but much more as the Full HD is yet to be adopted by major networks. It just changes our entire approach to documenting our wilderness areas and wildlife. This gives the common man an ability to create Hollywood quality clips, provided he/she understands its limitations and pushes the camera to the hilt.

The First part of the review is here:
http://www.indiawilds.com/forums/showthread.php?t=3194

The Second part of the Mark IV review is here:
http://www.indiawilds.com/forums/showthread.php?t=3372

Cheers,
Sabyasachi