Not sure if this post was joking, but there are plenty of worthwhile upgrades from the 5d2 to 5d3 they may just not have been what you want.
None I ever noticed when using the two. But of course YMMV. More precisely I'd say you would have to have a very specific reason to prefer the one over the other.
I did not not see any improvement in any aspect of my photographic results (it did however have some noticible improvements in its handling which I miss on the 5DII).
Not sure if you would say "very specific" but the improved AF, fps, high ISO, build and weather sealing along with bracketing are features I enjoy, oh and having a 100% viewfinder.
I think the AF improvements are the biggest draw card for me, this is a big part of the majority of my photography.
On the topic of a high megapixel camera, I can't see this being the 5d4 unless they have multiple models, or are creating multiple 1d series again.