My experience with the A7 is limited, so my opinion is formed from a perspective of instant impressions.
We know the image quality is superb, and the potential to create stellar images that can exceed the capabilities of the Canon sensor are fact. So that's out of the way.
I've been shooting professionally going on 9 years. In that time, I've only used Canon and the occasional Nikon from a friend - I didn't like them. As a professional shooter, and depending on the environment you shoot in, an SLR is a working tool that has a reputation for being reliable and supremely functional.
From this standpoint, there aren't many environments where an SLR wouldn't be the absolute best choice as your working tool. It's shortcomings are weight and size, but this is made up for by providing a build quality that has seen it survive drops from buildings, being covered in snow, drenched in rain, the list goes on. They're built to take the beating you throw at them and Canon Professional Services is there to ensure you're back out there making money again ASAP should something fail.
The layout of buttons and menus are a no fuss, get the job done style. In my comfort with Canon, I can change every setting without taking my eye off the VF, and the buttons essential for taking the shot are where they need to be for quick access. This is something that cannot be said about an A7 mirrorless camera. First, the original models had some quarky ergonomics that seem to have been mostly addressed in the latest adaptations - namely the shutter location and scroll dial.
Granted, with more seat time behind any camera you gain a familiarity, but the lack of buttons or placing them in less than desirable locations is a real issue in the field. A complaint most users would never have unless they're shooting run and gun, fast-paced subjects like sports, events, weddings, etc. The EVF isn't to my taste, but that's seems to be something you enjoy.
The smaller camera system has clear and obvious advantages over the larger SLR bodies, but I find myself looking at the complete system and asking myself if it can get all the jobs done for me. What happens when I'm at a wedding and suddenly the AF goes ape on a shot I know my SLR would nail? Would I then doubt the camera or question it? I'm sure it could handle an event just fine, but will it then work well enough with an adapted telephoto lens at a race?
For me, I shoot far too much variety in various climates. I don't really have the coin to blow on a camera that can't replace one of my cameras in my bag entirely...or begin investing in another camera system.
That said, grabbing an A72 as a spare to work alongside and gain familiarity with would be very nice. Just hard to justify when I'd rather have that new softbox, lens, case, laptop, larger budget cushion, etc....
Cameras don't suddenly begin taking bad pictures because something new and fresh comes out. I built a career off crop sensors and a "junky" 6D. If you feel it would make your job easier or improve your product, go ahead and make the jump. I don't feel it can do either of those things for me, especially when I never find myself second guessing my gear or work today...of course I want all the gear on earth though. Haha