Mirrorless is the future.
Mirrorless, even the Sony A9, is still in its infancy. Although, the A9 finally makes a few key advancements that brings mirrorless to the table for the first time, barely. Overall, mirrorless needs many generations before it is viable enough to displace DSLR in a serious way.
There are still more cons than pros to mirrorless, regardless of how unique and awesome certain features are (such as the viewfinders).
The cons mostly impact real pros.
With the rise and take over of camera market by cell phone users, the market for dedicated cameras is ever pushing upward toward the Pro range.
Mirrorless take over will be slow - because mirrorless ONLY features must prove to be of greater worth. This is a tough, slow sell.
Physics dictates that certain lenses cannot be made much smaller. And that certain lenses are required to achieve certain perspectives and looks in imagery. Their size and weight eliminates the benefit of smaller size and weight of mirrorless bodies.
To add to that, and to the cons that exclusively impact pros -- is the fact that some people do not want a smaller camera. They actually want a physically larger camera that is comfortable to hold all day, that fits the hand. Mirrorless options must be made larger (at least as big as a 5D4 w/ battery grip) to appeal to pros. I'd like to see 1DX sized mirrorless rig.
Disagree? I challenge you to mount a 70-200 2.8 and a 24-70 2.8 on your camera and hold it while shooting a minimum of 8 hours to simulate a wedding day or festival event. Don't forget putting a real flash on top. Tell me how your hand feels after that trying to hold onto the point-and-shoot/travel style body of the current mirrorless cameras. Yeah, and you'll need about 7 batteries too.
These bodies do not have a dedicated grip. Instead, you hold onto the end of the camera body. There is also the poor placement of controls, and cramped spacing. This is a big problem for mirrorless. Mirrorless will have to be introduced into DSLR sized bodies before mirrorless can conquer DSLRs. That is just 1 of many prerequisites that has to be met before the writing is on the wall for the demise of DSLR.
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I would like to see a future where the pro 35mm world has larger mirrorless camera bodies that accepts "sensor backs" like the medium format cameras do but of course on a smaller scale. This way, companies like Canon and Nikon, who are experts in photography - can focus on photography, not sensor design which is for the tech geeks and semiconductor industry. Decoupling the sensor from the body will be a comeback to the days of film where people had choice. Kodak vs Fuji becomes Sony vs Canon or Sony vs. Toshiba
Sensor manufacturers who specialize in this work become the new makers of film.
This is extremely unlikely. Such a thing would require that the DSLR world has been totally wiped out. And consumers are not using any dedicated cameras anymore, even mirrorless ones. That requires cell phones get better to the point that they've fully overlapped with the abilities of entry level DSLR's and mirrorless. Dedicated cameras become the realm of pros. And as such, economy of scale means camera companies have scaled back to just a couple of bodies only and it isn't economical for them to design, build or buy sensors anymore. Also, it would mean that the feature set of bodies in that distant future will reach a sort of practical limit. Meaning, FPS will be so high - they can all do any sports photography. AF becomes moot with high density AF points and complete coverage. And all the bells and whistles are all in there already. So that the need to update bodies becomes less important. We can see the very beginning of that already in DSLR's. The update cycles getting longer for Canon and Nikon, slightly - but longer. This effect will grow fast, leading to slower update times. Because cameras are getting stacked with powerful abilities to capture images to the point that the only revolutionary change will be to pull stills from video. Mirrorless that reaches 20+ FPS is just about in that realm.
That said, these are possible conditions that might need to exist for the possibility of such to ever happen.
Or, 35mm just dies off entirely and pros stick with medium format, whose prices will come down.
We've only seen about 10 years or so of smartphones. What will the next 10 years look like for their cameras? The innovation and evolution in their cameras has been significant and shows no sign of slowing down.
They never have to be pro level. All they have to do is reach the ability to make a Rebel or D3400 level camera obsolete. I see this as possible in 10 years from now. Once soccer-dad's DSLR's and mirrorless for that matter are gone from stores and won't sell -- the floor falls out from under the entire dedicated camera market. Enthusiasts and Pros are subsidized by these users.
What will delay this will be the hobby market. Those users who want to be creative and create images that cell phones can't because physics dictates certain lenses be used for which cell phone will never be able to. How many and how big this market is could vary a lot. Will be mirrorless only of course. I think it depends on the industry's ability to educate and market to a whole new generation or users the value and merits of photography. They have to build the demand and interest. They have to do that by emphasizing the differences and the quality and creative potential. The more and more society becomes accepting of cell phone quality and "look" in images, the more certain the death of dedicated cameras are. As this goes on, cell phones will slowly be able to replicate *some* of the DSLR look ...will it be enough? Depends on the users. For some it will, for others it will always be compromises. In any event, this becomes yet another way cellphones chip away at dedicated camera potential buyers. A little piece there, a little piece here. They don't have to completely meet all capabilities and win over all users, just enough to reach a critical mass that sends the already declining dedicated camera market to its death. A point where it isn't economically sustainable to create these cameras any longer.
Social media and sharing is with us for the long term. To this day, not a single dedicated camera has a decent, easy and reliable way to quickly share photos. This is a massive problem and the biggest engine driving cell phones ahead. Looking at how pathetically slow the innovation of NEW features are in cameras (existing features are advancing very well), it isn't on the horizon in the slightest that a dedicated cameras from Canon or Nikon will become Android based or have the capability to join cellular networks full time like a phone to make sharing seamless. These companies have no interest either. This would cost consumers even more money and require data plans. The convenience just isn't there no matter what they do. In this regard, they are doomed. Simple as that. The same way the very first sensor technology signaled the end of film, this is tech that will end most of the dedicated cameras.
Back then, there were tons of deniers. Film will be around for 20 more years they said. Well, it happened a LOT faster than they thought. Naysayers criticized early digital for having worse quality than film and weren't convinced. This was 100% true early on. This was completely true while we watched film die a quick death. The same is true today. Cellphones have crappy quality - sure, but convenience trumps all out quality. Never underestimate the markets response to convenience.