I am still more than satisfied with the images I capture using Canon equipment, and that includes using a new to me 1D.
I can't think of any compelling reasons to switch.
As compelling as the Sony A7 series seems to be, I am not impressed with the longevity of Sony consumer products. I may rent one next year and an adapter, but I do not see buying one.
I rented a Nikon lens with a defocus control and found it to be very interesting, but not a reason to switch because I can use it on my Canon
There are lots of other lenses that I can stick on my Canon with an adapter. Much cheaper than buying a new body.
Much harder to stick a TS-E or MP-E 65 on something else.
I remember taking lots of film pictures with a once new EOS 620 and marvelling at 3x5 and then 4x6 prints. Enlargements, even 8x10, never seemed to be very good (I never did the darkroom thing).
I can print way bigger than that now, from home, on almost any consumer grade inkjet printer.
I would need to improve my technical skills and creative views quite a bit to exceed the capabilities of the gear I have now.
I am kind of tired of the forum background noise that is demanding better stuff from Canon. While their needs may be genuine, their photographic styles or needs sure appear to be small (if not tiny) market segments.
The best way to get Canon to change is to stop buying their stuff.
Edit: Part of me would like to see a significant increase in megapixel count, but I know it will not be cheap and those megapixels will have added computer/storage costs.