The only way that it would be revolutionary is if Nikon crop cameras were destroying them. If that doesn't happen I would only expect minor improvements, but Canon will tell you the opposite (just like they are doing with the 5Diii).
I wouldn't call 9pt AF with a single cross-type to 61pt AF with 41 cross-type and 5 double cross-type, a 6fps frame rate, nor native ISO 25600 "minor" improvements...
The difference between the 5D III and the D800 is not that one has a bunch of minor improvements and one has a bunch of HUGE improvements. The simple difference is that the D800 has a neatly packaged "headline" feature...36.3mp. Thats it. The 1D X stole the 5D III's thunder with its ISO 51200, but that doesn't make the 5D III's major improvements "minor". They just aren't "headlines".
I guess I wasn't very clear. I'm not saying that the 5Diii ionic had minor changes, but as a whole it w only a minor update, especially after three years.
Major improvements would have been much higher MP while still having great low light capabilities. It would have also included things like 1080p 60 fps.
So like I said initially, the new 5D is in no way revolutionary. It has had some very nice improvements, but it's been three years, nice improvements are the minimum to be expected.
Either way, it's an awesome camera. There probably isn't much that really needs to be done to it, but the iii was basically just an update and not a revolutionary release.