Amaaaazing. Wow!! The crop mode on the D4 is truly incredible. It's a perfectly detailed 1080p image! Imagine combing that with the Atomos Ninja- you would be totally set...and also broke. The 2.7x factor on all your lens might be difficult to work around though. A 24mm lens would effectively act like a 65mm lens. Not too much leeway if you need to get a wide shot in a tight location.
Really it's a brilliant, creative solution by Nikon and they deserve major props for it. Of course Canon has considered this option as well, and could easily have added it to the 5DmIII but no, they have to protect their C300.
Too bad they couldn't include it on the D800, but the crop factor would probably be even larger than the D4's 2.7, since the D800 has 36 megapixels vs D4's 16.2. Probably to the point that it isn't practical.
One thing, I understand the D800 has a cropped DX mode for DX lenses. I'm curious if recording video in that mode would produce a sharper, more detailed image since it's downscaling less pixels. Please correct me if I'm wrong.
Competition- I love it! Nikon has really stepped up their game. With the D4's Crop Mode, Uncompressed 4:2:2 HDMI out, and the classy downscaling of the D800, I think Nikon has a very strong advantage over Canon in terms of DSLR video. Though Canon's DSLR may produce nicer colors and of course less moire and aliasing.
That being said, I'm still waiting for a proper color charts test of the D800 vs the 5DmIII head to head before making a purchase. Also needed is a proper color charts test of D800 internal codec vs Atomos Ninja to see how much more resolution and detail is improved by going directly to Pro-Res. (Sorry but that initial Youtube footage is totally comprised by YouTube's pitiful compression).