Nikon patents two full-frame mirrorless lenses: 52mm F0.9 and 36mm F1.2

Firstly, look through the viewfinder of a Sony A900, then add the Type L focusing screen. Now, that's what I need in terms of viewfinder.
Secondly, my remarks about the smartphone generation (yours, I dare to suppose, considering that you apparently stopped reading and went on the defensive) were not meant any more negatively than calling my own generation old farts - it was used affectionately. If you bothered to read the last two paragraphs you would perhaps realise that I advocate the use of EVF's.
You can't teach old dogs new tricks, they say. I say: Don't become an old dog at a young age.

There is no real reason Nikon or Canon couldn't make a mirrorless camera that uses the existing lenses mount and in fact I really want them to do so.

Of course using the existing mount will mean you wouldn't be able to reduce the size of the camera in the way Sony and Fuji and the like have been able to do so. This is a problem for some, but I don't really mind my camera being "big".

Well, the point about mirrorless cameras is that without the mirror box, you can make the camera less deep. Instead of a mount flange distance of 46.5mm you could have, for example, 18mm. You can fill this extra space with an 20mm adapter, which is essentially a hollow tube. This is, for example, how all the Canon lenses can be used on the mirrorless Canon EOS-M system. However, people don't seem to like such adapters that much, rather prefer lenses that mount directly. Lenses that mount directly, can then also be made smaller, mostly in the UWA and WA range, because of the shorter mount distance.
You could of course design a camera that keeps the original flange distance 46.5 mm mount. The body would be deeper for no reason, and you could not design the smaller UWA/WA lenses.

@JoaoPedroAB
You are right, current lenses should work on mirrorless.
But both designs presented here are IMPOSSIBLE with the F mount, so both lenses would add to the artistic arsenal of a photographer.

Moreover, specific designs may (or may not) be faster to auto-focus (smaller focus lens group) and/or smaller in size than their F-mount counterparts.

"... suppose, for instance, that Nikon goes to Nikon D6. IF there is no technical difficulty, they would have a choice: use mirror or mirroless technique. I guess that the latter is much better for several reasons (I use Olympus e-M1 and E-M5 ii). Professionals like large cameras, as you know. Then no problems on using the current lenses and using mirroless approach, they would get ride of the complicated mirror and would be able to increase (and much) the fps."

Nikon will likely never "need" to go to a mirrorless flagship (like your hypothetical mirrorless D6) because the lenses typically used on flagship cameras tend to be so large that the camera ergonomically needs to be large enough to accommodate a mirror box. And low mass mirror designs, with rapid actuators, will likely keep the FPS "fast enough." Plus, traditionalists love their optical viewfinders. However, the flagship scenario is a special case. Mirrorless is clearly the future, particularly as EVF tech evolves.

Pentax tried that idea, but the camera looked ugly to start with & defeated the purpose of going mirrorless with flange to sensor still being so long.

Because echosystems are based around mounts. Cameras come and go but the lenses are kept far longer and that finally the mount people buy in. Native support is also better than an after through adapter.

But you can pursue both of course. Where I am not convinced at all is that it allow for smaller lenses at all more than the sensor size. Overall the Sony FE lenses are big/jheavy and quite comparable to equivalent Nikon/Canon lenses.

Fuji X lenses are small but dedicated to APSC and if you see their f/2.8 zooms are big/heavy.

If you look at Pentax limited lenses all made for K-mount you get a variety of small, light, hight quality lenses from 15mm to 77mm including 4 pancakes. They even have a some moderately size zooms, a collapsible kit lens, a nice small 55-300 and even the f/2.8 zooms are not that big.

People value ultimate resolution for hypothetical 40x60" print seen with a magnifying glass... So mirrorless bodies get just that too.

Even bigger LOL, needless to say to can't read it seems, there in B&W 256.8mm in length. Wanna try that again.

Nikon 52mm Specs

ｆ ＝ 51.60 focal length
ＦＮｏ ＝ 0.91 (aperture)
ω ＝ 46.19 (half angle of view)
Ｙ ＝ 21.63 (image height)
ＴＬ ＝ 256.8 (total length)
ＢＦ ＝ 18.225 (backfocus)

Not sure if you're reading the patent specs correctly or not, but I would kind of expect a 50mm f/0.9 lens to be on the large side.

Sony is going the way of Samsung once Nikon releases their mirrorless FF camera!

panchorancho, if sony folds, Nikon will fold soon after. Remember where Nikon sources their sensors and where the innovations that make Nikon and others competitive.

In fact, if Sony was mean and not forward looking, Nikon, Pentax and others it sells its sensors too would be long gone. But Sony is smart. The normal mind set is you deprive your competitors access to the no 1 piece of the puzzle of a digital camera - the sensor. Without Sony, these companies would have probably folded a long time ago.

If you can't figure why Sony does this, then that's your problem. And Sony is not like Samsung. Sony has a loooooong history in digital imaging. it's not a beginner.

They would have found another image sensor supplier, then.
E.g. Samsung NX1/NX500 sensor has 28 mp, 15 fps and cross-type OSPDAF, which Sony doesn't have still and they put 24 mp with AA filter in their cameras.
Nikon exists because of fast AF and large lens portfolio, which has nothing to do wth Sony.

@catipellar Nikon doesn't need Sony, Sony needs Nikon! Without Nikon's sales volume, their whole division would go bankrupt! Learn basic economics 101 and come back to me when you want to have a discussion with an adult! Lol

@theprehistorian
do you mean rays hitting corners at shallow angle?
For the lenses pictured, this does not occur. It depends on position of exit pupil, NOT the rear element.
It's not major issue on BSI sensors anymore.

See Sony FE lens line. They are not any smaller than the DSLR lenses with same focal length and apperture overall.

The shorter flange allow for smaller design, but when you aim for ultimate quality, you may not be able to leverage that that much.

Mirrorless lenses are made with future technology, while regular lenses are not future proof. You can read more about it regarding the progress of Moore's Law and the dynamic physics of optical design. Basically new lenses do not have the reflecting mirror built into the optical flange path of the light ray emitters. Very simple when you think about it. Unfortunately Sony lenses are not true mirrorless since they do not give a proper 4k readout on the sensor to lens distance ratio. Properly calibrated lenses are more a specialty of Nikon and a few lens designs from Cosina Zeiss.

Assuming you ignore short periods where manufacturers can push a lot of units into the channels and then have some slower months afterwards, last year we had:
8,449,043 DSLRs shipped
3,158,735 mirrorless shipped = 37%
370,126,941k Yen DSLR shipments
149,432,809k Yen Mirrorless shipments = 40%
Jan-Jul this year:
4,322,753 DSLRs shipped
2,397,936 mirrorless shipped = 55%
199,784,763k Yen DSLR shipments
130,158,097k Yen Mirrorless shipments = 65%
But that will probably change in the second half of the year due to DSLR launches.

And you shouldn't expect Nikon to get it right the first time, a7 was pretty crappy first gen and Sony was all-in, Nikon isn't.

What about Pentax 31, 43 and 77mm Limited lenses?

You could tell 35 vs 36mm photo?

Because those are (exact) focal lengths extracted from patented formulas, not 'marketing', rounded focal lengths. Same for the max. apertures.