We can't make predictions on what kind of performance we'll see or what kind of performance future Nikon bodies may have using canon glass or Nikon glass. It may perform better, worse, the same, or depend on the lens and the quality of the reverse engineer as well as the fabrication of the adapter in question.That's the only variation that's actually plausible, although it still really doesn't make much sense apart for tripod use and the makers of lens adaptors, it's good business for them.
Even if they adapt it super well, is it going to be function any better than F-mount lenses, having better than 3-axis stabilization? No. But unlike those, will they support dual IS? No. Will they work like with DPAF? No, not even close. Is it going to be better for video overall? Probably not for 95% of the people and the rest have other choices than the EOS R.
Sony is supporting this idea because they didn't really have much choice and now it is simply better to use a native lens but they still sell cameras.
Nikon on the other hand sells other cameras and wants to sell lenses (any types that they make) and XQD cards.
There is also the question of where is Nikon going to take their AF system: 2017 saw patents for basically DPAF from Nikon as well as other multi-pixel PD patents. Obviously the recycled D850 sensors they used didn't have the needed tech, but it is a given DPAF or similar will happen, in addition to Nikon execs already saying "absolutely" when asked if there are pro bodies coming... So whatever issues today due to the camera or sensor tech, are less important than physical and electrical ones which tend to be baked in the mount standards and much harder to work around. But as we determined, EF-Z is one of the simplest adapters outside protocol conversion. But that's tomorrow's body talk, and speculative. how about today?
Even if Nikon has similar lenses and perform better, it doesn't rule out real cases for the adapter today:
1) you may shoot canon and wish to have a D850 sensor behind that glass. you may prefer the color science of Nikon to that of sony, and if the EOS-R body tomorrow isn't to your liking or the sensor lags behind again, you don't have to settle for sony. You don't have to sell your EF glass and buy Nikon F glass. you can always sell the Z body when canon catches up or keep it and get the next one.
2) you may want some lenses canon has that Nikon doesn't, or that they have but are too old, or no longer AF. There are not as many as there used to, but still there, specially some of the more niche ones. In particular consider D lenses like the 135 f/2. Nikon never updated it and no way they will. It will be a Z lens...someday. The D will not AF with the Z because it is a screw driver AF lens. What if you wanted it and you find a cheap copy online from a canon switcher? Just buy the canon!, the adapter and BAM, problem solved. You have a 135 f/2 with bloody AF. Is it as good as it would be on a canon body? who cares because it is better than the D lens that doesn't auto focus at all!. Off course you could just buy the 105 f1.4...but that's expensive.
I'm not saying those things will apply to everybody or that they are common. Only that if there is a market, people will seek to address it and that the pin layout isn't going to stop the various adapter shops form trying to address it.