I don't even know if it's doable in firmware, since I don't know any details about the DIGIC 4 architecture and what it has. But if they were to add this feature in firmware, I'd be jumping to download it and upgrade.
What I would like to have is for video to add some modes.
I'd like to see a matrix of all possible combinations of video geometry and frame rates be available for choice, regardless of the NTSC/PAL setting.
The frame sizes (geometry):
And for frame rates, I'd like to have a choice of both the NTSC 1000/1001 rates, and the 1/1 PAL rates. So this list would be:
60 (true 60)
50 (true 50)
30 (true 30)
25 (true 25)
24 (true 24)
All combinations that don't exceed the system speed capacity should be allowed (so 1920x1080p60 is unlikely).
I'd also like to see time lapse video modes (much slower frame rates). Of course, with a timer shutter release, it can be done as photos (already done that once).
FYI, a clocking frequency of exactly 120 kHz (or any whole multiple of this) can be divided by a select whole number and come up with all the standard video frame rates.