[obican]

Well Nikon and Canon themselves promised mirrorless bodies, theoretically adapters should be nothing but extension tubes, IMHO what might be lacking is automatic focus peaking, how would the camera know you are rotating focus ring in manual focus ?

First of all, it's Focus Magnification, not Focus Peaking. Peaking is the colorful help thingie and is always active as long as the camera is in manual focus mode. Magnification is only activated if you press a button or turn the focus ring.

Second, with Nikon it's not as simple as you think. While Canon EF mount is completely electronic, Nikon isn't and needs a ton of levers, feelers, switches and even electric motors to make their lenses work. If Nikon offers a simple tube of electrical contacts as an adapter, only a handful of their lenses will be compatible.

And for the camera knowing whether the focus ring is turned or not, it's not really that hard. Lenses transmit focusing distance to the camera. If it's changing = focus ring is being turned = turn on magnification. It even works with very old Sigma lenses adapted via Sony's own adapter to Sony bodies. Not a big deal.

Sure there'll be issues with some lenses as it doesn't probably work as simple as I've put it but still, no big deal. Worst case: press a button.

You don't want to try to manually focus on EF lenses anyway. 30 degrees of rotation