OK, I have only read part of this long thread, but here's my take :
I still own a 5Dc, passed the 5DII upgrade, since I didn't feel a need for extra resolution and was mostly interested in better AF, which did not happen on the 5DII.
So, as you might expect, I believe Canon should improve the DR of its sensors, not the resolution.
That being said, the 5DIII is everything I would have liked to see in the 5DII. So this time I will upgrade.
Sure, low iso DR matters and Canon deserve all the flak it is getting for not improving it. However, as I don't shoot much at 100iso and do a lot at 800 and above, I guess I am less affected by it than many. Certainly it would be good to have higher DR at high iso (much more important in my eyes than higher resolution).
One thing that gets surprisingly little attention is the silent mode in the 5DIII. For me, this is a huge improvement in a dslr. Mechanical noise has ruined more shots in my experience than lack of DR, simply because I had to stop shooting. It's distressing how little DR there is in a picture you do NOT take !!!
In an ideal world, I would like the DR of the D800, the silent mode, frame rate and AF of the 5DIII. I would also like the nikon 12-24mm in ef mount, along with my beloved 135/2.0L.
But as this is not an ideal world, as I have quite a bit of an investment in canon L glass, as photography is not my profession, as there is no way I can justify spending the amount to own two systems, I'll have to settle for the lesser alternative : just one lowly 5DIII.
Strangely enough, this is not making me particularly unhappy
Still, canon should be working on DR, and not just at low iso.