The next medium format camera from Fujifilm is expected to offer an even higher resolution than the expensive Phase One XF IQ4. According to the latest rumors from a reliable source, Fujifilm is currently developing a GFX camera with a 180MP medium format sensor.
I may not be representative of a larger sample, but I used medium format for landscapes, and always shallow depth of field. For sharper images, I used longer lenses on a 35mm camera. So, a diffraction issue wouldn’t be bothering me on a medium format camera, if I ever even found the money to get one.