the mirrorless cameras are a lot smaller and lighter so treating them as a DSLR accessory wise might not be applicable anymore as they might be kind off contra dictionary to downsizing the camera system.
Z 24-70/4 weight 500g DSLR 24-85/3.5-4.5 460g
Z 35/1.8 weight 370g DSLR 35/1.8 (FX) 305g
Z 50/1.8 weight 415g DSLR 50/1.8 185g
Next lens on the roadmap is a 58/0.95 which is likely > 1kg in weight.
There is as of now no evidence of lighter weight lenses for Z, on the contrary!
There are opposing trends in ILC lenses basically. One is to make for smaller and lighter weight, Micro Four Thirds and Fujifilm's offerings are along those lines, as are Sony's camera bodies and to a lesser extent lenses.
But there is another trend which is to maximize image quality in the presence of high-resolution sensors, and this leads to either extremely expensive lenses (Leica) or heavier and larger lenses (such as Sigma Art and Zeiss Otus) than in the past.
Nikon is clearly aiming to make higher quality lenses than previously and this means there won't be weight loss realized on the lens side, except perhaps in some wide angles which are not yet presented.
The camera body is lighter but since it seems to need a bunch of batteries this lightness is also perhaps not as much realized as some hope. Perhaps over time they can optimize power consumption and the firmware but it seems at first there will be a lot of people purchasing battery grips.
Furthermore the professionals who do photojournalism, event photography etc. are used to the f/2.8 zooms and I am betting that's what they will be using also in the future. Zooms are great for covering a variety of situations and going from an overview to close-up quickly, and many photographers need that capability. They also need it indoors which means f/2.8 is it. And the f/2.8 zooms will probably be similar in size and weight compared to DSLR offerings. The superwide angle is possibly going to be a bit smaller.
In other words I don't believe photographers will give up their f/2.8 zooms. And the bodies need good ergonomics for handling these lenses (and larger ones on the long lens side, i.e. 300/2.8 ).