If 5D3 only implements aliasing/moire free video and more resolution on video, I will be more happy to upgrade to 5D3. Even if this was the only improvement on the 5D3 over 5D2, it would be worth every cent.
The other thing I always of course would like to be improved, the dynamic range. It is more important than low light performance. I have been happy with the 5D2 dynamic range since it is much better on it than some other Canon DSLRs, but I would be really happy if it was pushed even greater since I always shoot RAW and edit every picture. That would make amazing possibilities for post-production for the kind of photography I typically do.
If thats all you want then look at the anti aliasing filter from http://www.mosaicengineering.com/
This plus a 5dmkii would be much cheaper! Id hope for other improvements such as rolling shutter, maybe 60fps 1080p, improved codec etc from the next model.
I'm definitely with you on the 1080p 60 and improved rolling shutter. Looking at the C300, I think Canon certainly have the capability to radically reduce rolling shutter, albeit that it'll be a bit trickier to control on a full-frame sensor with 22MP.
Speaking of which, I'm really happy to see the 5D III sit at 22MP. From a stills perspective, that will give me a native 13 x 19 print (as long as I don't crop too heavily) which is the biggest size that I regularly output to. From a video standpoint, 22MP just happens to be the magic number for exact 3x3 "pixel binning" (averaging over a 3x3 group of pixels) when down-scaling from full-res to 1080p video in 16:9 aspect. The 5D Mark II uses line skipping- basically ignoring every few lines of pixels, throwing away a huge amount of information. If this was in Canon's mind when they decided on the resolution, I think we could be in for massive leaps in video quality over the 5D II. I'll take pixel binning over line skipping any day!
I don't think the codec is the limiting factor in the 5D II; you can bump up the bitrate with Magic Lantern but, to my eyes at least, it doesn't really do a lot. I think it's held back more by its very rudimentary down-scaling method and native 3x3 pixel binning would definitely help there. The Panasonic GH2 employs smarter down-scaling and the resolution, aliasing, moire and high ISO performance are much better than the 5D despite its sensor being tiny in comparison. Imagine what proper down-scaling could do on a whopping full frame sensor! Once the down-scaling is sorted, the codec would be the limiting factor so I'll happily take pixel binning AND an improved codec!
The Canon 5D II is almost iconic for its role in starting the video DSLR revolution (with a nod to the Nikon D90 obviously!) so I've got high hopes that Canon will want to smash the pants off of the video quality with the Mark III.