The OVF versus EVF arguments are really more about nearly everyone trying to toss out multiple babies with multiple basins of bathwater...

DPReview tossed out some topical clickbait today about the death of the DSLR which was occasioned, I believe, by discussions they had with camera makers at a trade show in Japan. According the their various discussions the market for cameras seems to have reached a tipping point and the trends point to a rise in the acceptance of mirrorless cameras at the expense of traditional mirror bangers. Lots of people weighed in but most them seem side-tracked by tangential images that have little to do with the relative features and benefits of both types of cameras.

I believe that there are only two fundamental reasons why the mirror-free cameras will eventually become the more numerous and popular of the camera types and these two reasons have nothing to do with the presumptions of the general camera buyers.

First, I think the market is not driven by the camera buyers, as we often believe, but by the camera makers themselves. The camera makers, from Canon to Olympus, are ready for a wholesale change to mirrorless cameras because each camera requires many fewer parts and many less manufacturing adjustments in order to function within workable tolerances. If camera makers can maintain pricing within market segments while replacing higher cost DSLRs with lower costs mirror-free cameras they win on manufacturing savings alone. Canon and Nikon have always known this was the case but wanted to wait and see if the buying audiences could be willingly dragged in the same direction that the makers' accountant deemed more profitable.

As a sub-feature of manufacturing it is also easier to make smaller and lighter zooms and wide angle lenses if the flange to sensor distance can be reduced sharply (as in the design of most mirror-free, cameras). Being able to offer good quality (optical quality) lenses which are less costly to make (and ship) but which fulfill the same niches as more expensive to make lenses for traditional DSLR cameras is another profit plus for the makers.

There is something similar afoot in cars. Electric engines have far fewer parts than combustion engines and require orders of magnitude less maintenance as well. The result should be less manufacturing complexity and far fewer recalls and expenses. A plus for car buyers but a huge plus for car makers. (Note that the battery side of the equation is different from the issues involved in engines... don't argue the whole car...).

So, Canon and Nikon let Olympus, Panasonic and Sony work out most of the kinks of creating mirror free, interchangeable lens cameras and are now poised to step in and grab the lion's share of the profits. That's just the way it typically goes.  But it's important to understand that the simplification of the basic camera is a much bigger win for the makers than it is for the consumer who might have been quite happy with the older technologies. Mirrorless is not necessarily the way forward in cameras but probably seemed to Panasonic and Olympus, and more recently Sony, to be a way of using manufacturing costs efficiencies as a disruptor to the overall camera market. A way of dislodging the iron grip of the two comfortable leaders in the business.

The second fundamental reason people are moving from OVFs to EVFs is that being able to see in advance exactly (more or less) what you will see after you push the shutter makes iterative learning in the photographic arts much easier for people with little previous education in image making. Look at the little "TV" and turn the dials until you get exactly what you want!" Early acceptance of EVFs worked for people interested in video but at the time the video performance of mirrorless cameras was no great shakes (Panasonic GH series excepted). Perhaps that's why initial sales floundered.
Now that an EVF is for all intents and purpose the equal of the optical finders in most consumer DSLR cameras there is less and less reason for users to have a preference for traditional technologies and a somewhat more pressing case for always on live view. 

To serious amateurs and professionals the EVF offers a number of benefits but most of them are in the field of helping pre-visualize a final shot or in taking advantage of elimination mirror slap, and its attendant lowering of image sharpness, from lowering sharpness.

To hear the unwashed masses tell it these reasons are minor and the big differences between traditional cameras and the newer, mirrorless ILC cameras is all about the size and weight of the cameras. They could not be more wrong.

If that was all people cared about then mirrorless cameras would have died on the vine within a few years of their introduction into the markets, skewered on the sharpened pikes of many generations of cellphones.

Most people who buy stand alone cameras in addition to smart phones have, as their primary intent, the desire to take better images, and to take images that have characteristics that set the final images apart from what a typical user can get from a cellphone. Not just better high ISO/noise performance but also enhanced focal length ranges and better control over the results of depth of field decisions.

One can not help but notice that some popular mirrorless cameras (The Panasonic GH4, GH5, GH5S, G9, G8, the Olympus OMD EM-2 and others)  have grown in size and weight but have also grown in greater consumer acceptance during the same time frame. I also see many of the more serious mirrorless cameras, like the models I listed, being used frequently with battery grips to actually enhance the camera's handling performance by increasing its overall size. At the same time you've probably noticed that Canon and Nikon's very capable entry level DSLRs have shrunk down to the point where they compete, on physical volume, with most mirrorless offerings.

And while these smaller DSLRs are, in terms of overall image quality, very, very good you don't see many professionals and serious hobbyists rushing to dump their much bigger "professional" cameras in order to embrace the benefits of the single metric of size. Diminutive is not all it's cracked up to be.

It would be folly for camera makers to listen too earnestly to a vocal few who have determined that small size is the compelling reason for the market's embrace of mirrorless cameras. Reflexively making cameras smaller and smaller, without mindful regard for "haptics" and performance is the epitome of tossing the baby out with the bathwater.

All the Nikon and Canon have to do to overwhelm and re-dominate the market is to repudiate the trend towards tiny and instead replace expensive optical viewfinders with state of the art EVFs in the models that work well today. The Nikon D850 has been in high demand and short supply since its inception. Transition that picky market segment by creating a twin product that uses an EVF instead of a moving mirror and prism. The same across the entire line. Let buyers vote with their credit cards.
I'd vote for a D850evf over a plain D850 any day of the week.

The Canon advanced amateur line could be overhauled in the same way. In either the Nikon or the Canon camp or both they could retain their lens mounts if they wanted since it's my belief that the desire or demand to be able to use all sorts of legacy lenses is, frankly, much overblown on the web.
I'd conjecture that most users, especially in the younger audience segments, are generally less interested in using old, crusty manual focus lenses that we remember from out initiations in photography than we avid practitioners of a certain age profess to be.

A Canon 5Dmk1V or a Nikon D750, fitted with an EVF would become a better video tool, a more practical educational took and still, with PD focus on chip, be able to handle traditional DSLR strengths like continuous AF for sports.

Canon and Nikon benefit by being able to offer more things people seem to want, such as faster frame rates, more finder overlays, continuous live view while holding onto their embedded audiences by dint of those audiences' lens investments. They can attack previous mirrorless competitors head on, with the same features and performance options while still offering a vastly bigger selection of dedicated lenses which are optimized for their mount and their systems.

Canon and Nikon could also benefit by having their most advanced models available in two styles; with and without EVFs. The OVF version would become deluxe and limited edition tools of a certain percentage of users, continuing the halo effect enjoyed by both in the sports arena with very little downside.

Sure, a Sony, Olympus or Panasonic camera might let you use a Nikon 43-86mm zoom on the front of it but...would you really want to?

Nikon should have learned the hard way with their first mirrorless foray (V series) that tiny isn't necessarily the first feature most serious users demand. In fact, for sheer handling something like the Panasonic GH5 is the smallest camera that still feels reasonable comfortable and well laid out to me...

I think we're counting down the months until we see the vision laid out for us by Nikon and Canon for the replacement of their cameras in the $1000-$6000 price range. I'm hoping they don't base their market research on the whims and unicorn chases over in the forums on the world's most contentious camera website. I'd hate to see un-holdably tiny camera bodies and a raft of equally tiny and bland little lenses as the offerings for the future.

Big and bold is good. With electronic viewfinders it could be even better. And all that legacy glass....

What do you think the camera future holds? I hope I'm able to buy stuff that's big enough to wrap my hands around. I'm tired of the miniaturization compulsion disorder amongst some users. Let's not sacrifice good ergonomics just to add some mostly useless features.