No, I would not dump my Canon DSLR cameras (6D2 and 7D2) for a "CANON" or "NIKON" full frame mirrorless camera but, I am seriously considering switching to the Sony mirrorless system.
I have been severely disappointed with the Canon 6D Mark-2 and the full frame Canon and Nikon mirrorless offerings are, IMO, a big joke for top-line 21st century cameras.
I have recently purchased a Sony A6500 and have fallen in love with this little camera. IT IS EXCITING AND FUN TO SHOOT!
I love many things about the A6500! In fact, I like shooting portraits with my Canon 85mm f/1.8 lens and the A6500 with an MC-11 adapter better than shooting with the 85mm f/1.8 on the Canon 6D Mark-2 simply because it is easier to focus.
The 6D2 has its AF array crammed into the center of the frame which makes it impossible to place a focus point over the subjects eye/eyes during head and shoulders portraiture when using the eye level viewfinder.
Sure I can focus and recompose just like I could use cut film in my Graphic cameras but, IMO, technology has passed the focus and recompose point.
Sure, I can use Live-View and face detect on the 6D2 which works just fine and I can place the focus anywhere in the frame but AND THIS IS A GREAT BIG BUT, since I can only use face detect with live-view, I have to frame my subject on the camera's LCD which (for me anyway) is impossible in bright sunny conditions.
I can use face detect with the 85mm lens on my A6500 while still using the eye-level viewfinder! It works great but, what works even better is using a native Sony lens with Eye-Focus. IMO, this is the way to focus on people in the 21st Century.
I have also been shooting a lot of portraits with the Sony 50mm f/1.8 OSS lens on my A6500 and it works brilliantly! However, I can also focus on portraits very easily using a manual focus lens with my A6500 with a combination of Focus Assist and focus peaking. This allows me to use a large variety of manual focus lenses. I presently have a 58mm Russian Helios f/2 and a unique 75mm f/1.7 Night Owl lens designed for security cameras. Both of these lenses bring a very unique took to their images at an exceptionally low price. I have just a little over $100 dollars invested in these two lenses and their adapters.
I am seriously considering getting an A7iii with the Sigma 85mm f/1.4 ART in a Sony mount!