Convergence has become something of a buzzword in the industry. Unhelpfully, this is used by different people to mean one of several things, including the convergence of DSLR and mirrorless technologies or the convergence of stills and video cameras. (Few people are in a comfortable enough position to even joke about the convergence of digital and film camera sales.) It’s the first of these options that has had me thinking of late.
Although mirrorless cameras have historically been seen as an entirely distinct type of camera, that difference is narrowing. Obviously we've seen the body styles of mirrorless cameras start to converge with DSLR styling (though it's worth remembering that the very first mirrorless camera* - Panasonic's Lumix DMC-G1 - was DSLR-shaped), but huge strides are being made in terms of capability. Very early on, mirrorless cameras matched and overtook the most popular DSLRs in terms of single-point focus acquisition speed. Now, thanks to their full-time monitoring of the scene in front of them coupled with the development of on-sensor phase detection that makes them depth-aware, the best mirrorless models are starting to chip away at one of the last big areas of DSLR supremacy: continuous autofocus tracking.
The Samsung NX1 has helped change our expectations of mirrorless camera performance. Its subject tracking and ability to maintain focus on moving subjects makes it almost indistinguishable from a similarly high-end DSLR.
But convergence has come from the other direction, too. DSLR live view and video have tended to be a little clunky, partly due to redesigning the camera to operate with the mirror held up, but also because DSLR lenses aren't designed to be driven for contrast detection autofocus. However, the Canon EOS 70D's dual pixel AF sensor, plus the development of an increasing number of STM lenses, helps it offer some of the best video AF on the market when essentially acting as a mirrorless camera.
Then there's the Samsung NX1. It's is the size of a DSLR; it looks, feels and behaves like a DSLR. In almost every respect, it may as well be a DSLR that someone simply forgot to put the mirror into. I find it hard to look at these cameras and not think that the line between mirrorless and DSLR is being blurred, if not obliterated.
I think it's telling, though, that as well as adopting 'Mirrorless' (as shorthand for Mirrorless Interchangeable Lens Camera) as its preferred terminology, the Consumer Electronics Association also chose to adopt an umbrella term, 'ILC,' for describing both classes of camera regardless of technology.

Still a ray of light for the DSLR

There are still some differences that may never be fully eliminated. Because DSLRs' sensors aren't switched on for nearly so much of the time, they aren't nearly so demanding on batteries. This disparity is made larger by mirrorless makers using smaller batteries to ensure a body size advantage, and arguably exaggerated by the way the CIPA standard enumerates this. But if you need to shoot all day and not worry about battery, you probably still need a DSLR. Then, of course, there's the use of optical viewfinders. The quality and utility of electronic viewfinders has leapt forward generation to generation, but some users need (and some users simply prefer) the real-world view of an optical viewfinder, along with the shorter blackout times they currently offer.
It's likely that there will always be some people who simply prefer to be shooting with an optical viewfinder. Photo courtesy of Nikon
Finally, DSLR AF tends to work better in low light or with extreme defocus (typical when shooting with long lenses) than the current mirrorless cameras can match, but there could yet be technical solutions to close that gap.
For these reasons alone (quite aside from the market dominance still enjoyed by the two biggest DSLR makers), the DSLR will continue to carve out a niche for itself. However, we've recently seen the Sony a7R II autofocus Canon DSLR lenses at around the same speed as a Canon DSLR but without the need for AF microadjustment that high resolutions are revealing. If this technology lives up to its promise and trickles down into more affordable models, the DSLR seems unlikely to enjoy its mass market dominance forever.

Convergence and differentiation: one size fits all?

While for some (much?) of the market I think that the distinction between mirrorless and DSLR will become irrelevant, I don't believe there will be complete convergence. Having pointed out that there are areas in which DSLRs will continue to offer advantages for some people, I think there are other niches that could be better addressed with mirrorless cameras.
For many years, most of the major manufacturers have tried (and, it seems, struggled) to make mirrorless attractive as a step-up camera for point-and-shoot users. The logic was that mirrorless cameras could be smaller, lighter, cheaper (to make, at least) and provide a more compact camera- or smartphone-like experience. It seems reasonable enough, except in most markets, people didn't buy them.
Most manufacturers have tried to create mirrorless cameras for point-and-shoot upgraders. This publicity photo gives you an idea of who they've tried to target. It hasn't been terribly successful. Image courtesy of Olympus
Perhaps it takes more than a huge picture of Ashton Kutcher (a 'popular' actor of sorts, in case you've forgotten) smiling winningly from an end-of-aisle display in a big-box store to overturn a 'proper photographers use DSLR-shaped cameras' mindset. Or perhaps the camera makers, having learned the error of selling indifferent compacts based on cost rather than quality, were hoping the benefits of small mirrorless would mean they didn't have to under-cut DSLR pricing to make their products appealing. Either way, it's failed.
But those potential advantages do exist. Smaller-than-DSLR models have successfully sold to enthusiasts looking for a second camera or a primary camera that's more portable. And, based on the number of friends I have who don't consider themselves photographers but want something small that takes better photos in low light, I still believe there's a market beyond the enthusiast. But in this market, the competition isn't DSLRs — it's the convenience of smartphones. And its going to take more than a grinning cut-price Keanu Reeves to get the message out to a wider audience.

So you're pro-mirrorless, then?

This belief in convergence has already got me into trouble. I caused some consternation by pointing out that if you're looking for an enthusiast ILC, the Nikon D7200 is one of the bulkier options. But this isn't because I'm anti-DSLR, it's because I believe that the distinction is becoming irrelevant for an increasing number of people and so both types of camera need to be compared on the same basis.
Was this image taken with a DSLR or a mirrorless camera? If you can't tell from looking at the final image, does it matter?
Now that the feature sets of mirrorless and DSLR have converged to a large degree, it's reasonable to assume that plenty of would-be buyers will be looking at both mirrorless and DSLR models. At which point, it's only proper that we try to spell out the differences between those models. If it's fair for us to point out those mirrorless cameras that fall short in terms of battery life and continuous autofocus (when compared to DSLRs), then it's equally fair to point out that you sometimes pay a convenience cost for choosing most DSLRs (though this factor isn't represented in the final score nor in the reviewers' choice of award). This shouldn't be taken as endorsement of one technology over another - just highlighting a difference between one camera and its ILC peers.

So what does convergence mean?

I'd argue that the arrival and development of mirrorless has made all cameras better. Convergence not only means mirrorless cameras coming closer to matching DSLR strengths, but also DSLRs having to raise their game to withstand this competition and add features such as face detection that they haven't traditionally been able to offer.
Does this mean the DSLR is dead? Don't be silly. But I'd argue that in time, the DSLR will become a niche product, as will the differentiated mirrorless. Instead, convergence will mean greater choice and more capable cameras for everyone. Long live the ILC.
*No, I don't consider rangefinders to be Mirrorless cameras. Partly because their viewfinders are just as packed with mirrors as SLRs' are, but mainly because we coined the phrase mirrorless specifically to refer to the type of camera heralded by the announcement of the Micro Four Thirds system.