While I don't disagree with your theory on adapter vs native lens quality I still fail to see how this industry change to mirrorless is a foregone conclusion. Other than my little Canon M3 I've never used one, certainly not of the quality of the current Sony offerings. That being said, I have no intention of switching to mirrorless at the current time or in the foreseeable future. Personally I love having an optical viewfinder and have yet to see any reason to change that. I use LV quite a bit as well, but not for the same purpose.
What are the definitive reasons that a lot of people believe DSLR's are just going to go away? Based on what I've read, there are still some issues with EVF view finders. I understand some people prefer the smaller/lighter bodies but I also see many people that want their OVF and aren't bothered at all by current DSLR body size and weight. Myself being one of them.
So what you are saying is true in concept, but it only applies if manufactures stop making DSLR bodies, and I for one am having a hard time seeing that happen. I shoot Canon, and while that gives me some bias, it is only because of my current lens collection. Sony has some great bodies, not my style, but I can acknowledge that they are great bodies. Nikon is the same, they have some great bodies. So does Canon. There are small differences in high ISO capability and low ISO DR but those windows are pretty narrow these days. That leaves (for the mirrorless argument) that the EVF and weight/size being the primary motivators for going that direction and I just don't see it as a preference that will take over the market completely.
Sensors can be the same whether the camera is an SLR, mirrorless body or fixed-lens point-and-shoot. The three main advantages of mirrorless are EVF vs OVF, AF and video.
Once you can make an EVF with imperceptible lag (which has now been achieved), EVFs are a lot more capable than OVFs. They work a lot better in the dark - once it gets dark enough, you can't see anything through an OVF, while the EVF can just increase the gain. You get some noise, but at least you can still compose and focus. They can give true, through-the-sensor feedback, giving a true representation of what the final image will look like, brightness, colour, contrast and all - rather than just composition, they also give information about exposure (an SLR's meter can give you a weighted average, but doesn't tell you anything about dynamic range or whether parts of the scene will be blown out). They can be configured to display things like histograms, shadow/highlight alerts, focal planes, etc. The most you can do with an OVF is make it big and bright, and you can do that with an EVF too (and make it even bigger and brighter, along with all the other advantages).
Mirrorless AF has a lot more potential than SLR AF. For the most part, SLR AF is 'dumb' AF - it focuses on whatever it's pointed at and tracks it based on change in distance, rather than by subject recognition. There are some AI-based modes, using a low-resolution metering sensor, but these are limited, and restricted to the part of the frame covered by the AF system. In contrast, a through-the-sensor AF system can use both 'dumb' (PDAF and basic CDAF) and 'smart' AF systems (subject recognition, of which face detection is just the most basic) equally well. The 'smart' tracking systems are only going to get smarter and more versatile as processors and software improve, while you can't really make the 'dumb' systems much better - they already pretty much focus instantly on what you point them at.
Connected to AF, mirrorless video also has a lot more potential than SLR video. With the exception of cameras with a pellicle mirror, video is always shot in mirrorless mode - a mirror just can't move fast enough to shoot 25fps or higher. The camera is then reliant on on-sensor AF for focus - without the mirror in place, the off-sensor AF can't work. Thing is, all a mirrorless body's AF is on-sensor - the AF system remains fully functional while shooting video. The SLR is reduced to whatever on-sensor AF capabilities it has - with the exception of Canon's dual pixel sensors, this is usually not a great deal. This also has an impact on action stills photography. An 8k video camera capable of full AF capability while shooting video is also a fully-functional 39MP/25fps action camera. And that's not very far away.
Until this year, the main technological (rather than cultural, e.g. the insistence by some that mirrorless cameras need to be small) holdups of mirrorless bodies have been slow AF and EVF lag. Both have now been addressed.
How much better can you make an SLR, that you can't also do in a mirrorless body (i.e. not the sensor, since that can go into any camera)? Not a great deal. So, once mirrorless definitively surpasses SLRs in all these things (they have already reached parity with the top tier of SLRs), manufacturers are likely to mostly stop developing SLRs. There just won't be any reason to make them, apart from backward compatibility with vintage lenses (which Nikon/Canon won't be selling any more, so won't be making profit from) and appealing to an ever-decreasing cohort of technological Luddites.
