I'm demoing the Z6 and tried the MF Nikon 50mm 1.2 Ai-s with FTZ adapter and the Nikon Nikkor AF 50 mm 1.8 S. Here's my initial impressions...
The viewfinder is outstanding, very much like the Leica Q, but better. The build quality is also excellent with almost perfect ergonomics like the Hasselblad X1D. The MF 50mm 1.2 Ai-s is so much easier to use because of the ability to zoom in and focus right off the sensor, so I would imagine that adapted manual lenses should be stellar on this camera. The new Z AF 50mm 1.8 S is extremely sharp and absolutely silent in use. I was amazed at the quality of images and tried specifically to incite CA with backlit subjects and using f/1.8, but couldn't find any chromatic aberrations at all using the S lens. Even the MF 50mm 1.2 was simply outstanding in it's sharpness and color. One thing I did notice when shooting with the new Z 50mm 1.8 S lens, was in two sequential images I switched from MF to AF and the WB changed slightly from cool to warm. The images were taken just seconds apart, but showed the slight temp differential nonetheless. That was the only oddity so far, but i'll try to shoot some portraits using strobes to see if that WB shift occurs when switching from MF to AF in the studio. If Nikon would announce the upcoming 85mm 1.8 S, it would fill a gap for needed native primes lenses and round out the trio nicely.