422 video with real 1080p without aliasing/moire would be really nice. Based on my personal testing, the 5D resolves significantly more than the 7D, but still it is not true 1080p. This is also evident on the recent Zacuto test. http://www.zacuto.com/the-great-camera-shootout-2011/episode-two
The problem for Canon is though that the cinematography folks are already buying Sony FS100 and Sony F3 and leaving Canon behind - the ideal release time for 5D mk III with this would have been early this year and not early next year. And from technological standpoint should have been feasible target for some big corporation like Canon. The Zacuto test kind of illustrates how ridiculously low the resolution really is on the Canon DSLR video compared to a competition with cinematography cameras. I think the low resolution, aliasing and moire are the biggest problems in Canon DSLR video at the moment.
Well, at least I may buy the 5D mark III then if it lives to the hype in video quality because I am not in financial situation at the moment to both purchase FS100 or F3 and then also possibly replace my lens collection at the same time. I rather want EF-mount version and I am hoping it someday arrives. But Canon has succeeded to disappoint before, like 1D MKIV has really poor resolution compared to 5D mk II video and it came after 5D mk II. The aliasing is more severe and the resolution is barely SD. You can also see that by yourself in Zacuto test (link above). In other words it got worse. What guarantee there is that it does not get worse again with the 5D mark III if they treat the video as worthless add-on feature where consumer grade is ok and no professional quality is required.
And also I want to shoot still photographs and video with the same camera because I could not carry around when traveling both. I am already exceeding the limits of carry-on luggage in airlines. Last time it was quite tricky, they almost forced me to put expensive and fragile camera equipment to check-in luggage (where they would have been got destroyed most likely as a freelance/hobbyist I do not have heavy-duty camera cases for this purpose, and even if I did, what guarantee there would be that they would arrive undamaged and I would not anyway have more allowance for check-in luggage than the 20kg limit (44 lbs) - on my last travel they had opened my check-in bag possibly because they saw the steadicam and rig in the X-ray, if bag gets inspected, what guarantee there is that it is properly packed again and there will be no damage to fragile glass and the interiors are carefully inspected rather than just thrown back). I can barely get the 5D with lenses in the check-in luggage but it would be about impossible with the size and weight of Sony F3 (or Canon equivalent, if such camcorder would surface). I would prefer the DSLR form factor, otherwise the agility will be greatly reduced and I would no longer be able to document my travels even if I could make perfect video with it at home. A EF-mount DSLR which would do 422 or even better 444 video with real 1080p would be excellent replacement for my 5d MK II. If it had HDMI output with clean 444 it would be even better, then I would use Atomos Ninja to record the stream and I would get ProRes files directly without time consuming transcoding from h264 to ProRes before editing. Then if this camera would have higher video resolutions than 1080p, it would be nice of course. With 4K one can shoot exceptionally perfect and sharp 1080p, even if the 4K had some aliasing problems etc., the delivery format being 1080p would mask the problems that can be seen on 4K monitor.
What it comes to OLED: cinematography people are using external monitors anyway. The internal monitor being OLED would be nice, but it is not a killer feature that would make to buy the camera. There are many high resolution OLED displays out already in Samsung and Nokia phones (like Nokia N9 MeeGo phone) and it would be quite possible for such display to be on a camera. However, end results are most important from camera and for manual focus pulls in video a bigger monitor is very much necessary, for me it is almost indifferent if the display was OLED or not. Also the still pictures from the current 5D mark II are about good enough and even if there was some room for improvement, it does not make me to do urgent upgrade. If the still section would upgrade, but video section would remain the same or get worse (like in the case of 1D MK IV happened), that would not make me to do upgrade. Perhaps I would need to start considering the plastic ugly GH2 and go for M42 despite of the drawbacks of the smaller sensor then. I would dislike that, but if Canon would not upgrade video for 422 + no aliasing/moire + real 1080p resolution (resolving full 540 line pairs vertically and 960 line pairs horizontally), it would be like a message from Canon "We don't want you. Go for Panasonic now and put the hack on it to make it a proper video camera".