Landscape, architecture, fashion, product photography.I doubt Canon has figured a way to make a 70+MP with DPAF and 1D X performance so what professional is this for?
Low light will be as good as anything else out there. The lower resolution = better low light performance is a myth for stills (though not for video). At 70mp this thing would probably have a 35-40mp MRAW mode so a wedding photographer could shoot 70mp still and posed shots and 35mp for everything else to manage file sizes.Ok sure they finally put the dual card slots but do wedding photogs want 70MP shots (let alone low light performance)?
A good friend of mine specializes in wildlife photography and has great work. He's never much cared for fps and once told me 4-5 fps is all you really need. I'm not going to completely discount higher frame rates for wildlife and sports, but I also can't find any issue with his work, so....Wildlife shooters would like that res for cropping but if it's no better performance than the EOS R then that's a bust.