I would rather have 36mp than have diffraction kick in at f5.6.
Not sure what you mean by "kick in", but there is ALWAYS diffraction, at all apertures. The "diffraction limit" is not a limit. It is a calculation assuming some things about the Airy disk. The resolution of a photo, at the focal plane, is determined by pixel pitch, diffraction, motion, and aberrations. Slightly away from the focal plane, resolution improves by stopping down way narrower than f/5.6. Many of us routinely select f/11 or 13 as the best compromise when shooting macro on an APSC sensor.
Also remember that it's the lens that creates diffraction, not the sensor. Having more pixels doesn't increase diffraction. But you can see its effects better by pixel-peeping.
As long as I can remember (which for me goes back to 8 mpx cameras), there have been fears about noise and diffraction with higher pixel count cameras. Sensors now have an order of magnitude more pixels, yet IQ keeps on improving.
So it seems the camera manufacturers know what they are doing.
I'll be one of the first in line for the R7 II if it has the rumored improvements, and for me, the more pixels the better.