Glen, I use several Canon bodies, a 5D Mk IV and a 1DX Mk II are my main ones, but I also use a 7D Mk fairly often, and I use a 70D as a walksabout snap shooter when I want to just travel fast and light. So the app you suggested may work fine for me - I do have a mini IPad 4 that should work very nicely. I just need to figure out how to mount it in a hot shoe. Canon is selling 7D Mk IIs with a SD style card with WiFi that should link with an iPad easily too.
On different note, I spent some time reading about the new Olympus body but may just settle for a Panasonic DC-G9 due to its lower cost and a similar number of pixels