Who you calling layman?
I think dual cards is how Canon defines it. Probably Nikon too as the 750 does a good enough job to qualify.
So if I'm reading you right, your call is between the 5D series replacement and the 1D series replacement coming next?
We've done this before, but the ability to double or triple down is okay by me, and apparently you too. lol.
It all boils down to the processing power Canon can squeeze out of Digic and its own development team. I don't have faith they can focus track and shoot at 1D levels on a mirrorless camera.
PSA: The above post may contain sarcasm, reply at your own risk | Not in gear database: Auto Sears 50mm 2.0 / 3x CL-360, Nikon SB-28, SunPak auto 322 D, Minolta 20