I'm professional photographer who is using Canon 6d for 2 years already, over 100 thousand shots. It is fantastic camera but now it is in the end of its production term, and I think Canon will release 6D mark II next year. If so, here is list of desired upgrades, ie what I think 6d mark II should look like:
1. Articulating/Tilting screen. It is very handy feature allowing to use live view mode for precise non center focusing, no need to lie on the floor, you can shoot concerts, events inside crowd of people simply by holding camera in raised hands, yes it is required for pro shooting as well as for enthusiasts.
2. 7 frames per second shooting. 2nd big limitation of current 6d, low frames per second is bad, especially when competitors have 15 fps.
3. Built in Intervalometer. Cheap software realization, but it is very handy to have it built-in, for timelapses and astrophoto, rather then using external device.
4. Focus Peaking. Extremely useful feature, even with autofocus lenses. It allows not only to focus precisely but also teaches photo and videographers how to use their glass precisely, showing real depth of field.
5. Easier WiFi initial setup. I've no problems with it, but several of my friends had troubles and were unable to setup wifi on 6d due to its complexity. Less options per screen and step-by-step automated wizard with in camera help showing how to setup mobile phone or tablet will be fine.
6. 22-24 megapixel matrix with little wider dynamic range, +0.5 ev is fine (just to kick Nikon's ass:)).
I guess you can wish all you want. But in reality there is only one 'true' pro camera in the Canon line. The 1Dx. That is what a pro camera looks like and how it is built. IMHO, the 6D is not a full on pro body. It is an entry level FF for folks that don't want to drop the dime on a 5D Mk III. It is more similar to the 7D series than to the pro series.
Sounds like you really want to be in the xxD series IE like the 70D.
Im not saying 6d is a pro camera, only that it is used by both pros and non-pro photographers. Concerning xxD series, yes it has articulating screen, but its ISO performance and image quality overall does not match FF camera. So it would be nice to have FF camera with pro level IQ and handy ergonomics of xxD cameras.
So what you really want is a FF xxD.
Yes, a full frame 70Ds.
Though I would prefer the current GPS and no built in flash of the 6D, over the built in flash and no GPS of the 70D. Otherwise, things like the tilt swivel screen, 19 point AF system, FPS of the 70D would make a nice upgrade to the current 6D. I doubt we'll see the Dual-Pixel AF system in that level FF camera though.
And honestly I don't think the 6D ever should have had an XD moniker, other than the full frame sensor, it is more on par with the XXD, or even T6s level cameras.
And as to the increase in dynamic range, I haven't had any issues with the dynamic range of the current 6D.
I want 6d mark II, entry level FF camera, without 14fps, super autofocus or precise white balance of a pro camera, but with handy features like 70d has, ie relatively low weight, articulating screen, built in WiFi, GPS, intervalometer. xxD series is handy, but it has poor image quality compared to FF, far lower tonal range, ISO, crop factor, so this will still be complete different products.
Don’t think built-in flash is required, since you can buy separate small and light fill-in flash like 90ex.
Funny your original post mentioned so many things but made no reference to better AF. Virtually every other person who has undertaken to list needed 6d2 upgrades have led with better AF. My own list certainly does. I would like to be able to trust outer AF points at narrow DOF apertures but I don't trust them for that on 6d1. How about even 50 or so points, ALL cross type ?
However you want to categorize it, a full frame camera that costs $1,400 should not have just 11 AF points with only one cross type when a Rebel T6i has 19 all cross type.