Just like stills on a crop vs FF, you just get a wider and slightly faster lens to get that look and combat the crop video effect.
In practice this can get annoying.
Casual shooting, I may have a simple 50mm. The simple aspect ratio crop already makes me back up for video, a full crop factor would mean that I would need another lens.
Just my take on the 4k issue. If you are shooting your camera for anywhere from 3-5years before upgrading you want to have some semblance of future proofing. Everything is moving to 4k whether its necessary or not so canon could have included at least some kind of 4k video, even 24p should work for most situations.
As for everything else we really need to wait for user reviews. 45af sounds great but I even 9 points all cross type further spread apart would be better. 1/4000ss? was that really necessary?
However, heres to the 6d2 having really good files to work with.
No doubt that this is currently the best cam for the price. The question is how it'll hold up to Nikon's offerings.