Also, since the 6D doesn't have the AA filter there is tons of moire. Honestly, it makes a lot of footage look like crap
Unfortunately, you're wrong - the 6d does have an aa filter that also makes still shots softer, the moire is the result that downscaling to hd resolution cannot use "pixel binning" like on the 22mp 5d3 but needs to interpolate some of the 20mp lines - and the 6d is very bad at doing this.
They could just as easily do exact pixel binning on the 6D. They would just have to crop the image first.
- At 720p, the sensor is 4.275 pixels per output pixel, so you could throw away the outer pixels (use a 1.07x crop factor) and then scale 4:1.
- At 1080p, that approach would be more problematic, because the ratio is 2.85:1. Making it 2:1 would be a 1.43x crop factor, making it almost like shooting video on a crop body in terms of what it does to your field of view, but it still might be worth it if the results had less moiré.
With that said, it isn't just a question of binning. If you just bin a bunch of pixels together, you'll get more moiré, not less. You have to do the binning in combination with a digital low-pass filter that effectively does the low-res video equivalent of what the antialiasing filter does for stills. The real question is whether the 6D has the CPU power to do the low-pass filtering. If it doesn't, then binning won't help. And if it does, then someone could probably come up with a better algorithm for non-integer downsampling than whatever the 6D currently uses, resulting in video that is comparable to what you'd get with binning, but without the field-of-view change.