Several years ago I had my first introduction to mirrorless cameras when a friend showed me his Sony NEX-7 and I spent a few minutes handling it and noting the features he helpfully pointed out, including the interesting "focus peaking"...... I loved how small and light the camera body was and also the lens he had on there. The very next week I went out and bought myself a NEX-7 and a few lenses....
Over time I also added the wonderful RX100 series of cameras and eventually the amazing RX10 M4, and liked each of them for their versatility. I found that I was using my Nikon gear less and and less and picking up the NEX-7 more and more, and as time went on, the other cameras, too. When Sony released its A7 III I started thinking in earnest about selling my Nikon gear and just going all-mirrorless, but it wasn't something I was going to jump into immediately; I spent a lot of time waiting and watching and changing my mind from an A7 III to the A7R III and then waiting and watching some more as Nikon announced its new mirrorless Z series with accompanying lenses and an adapter.....
I knew that I did not want to continue having two separate systems and that whatever I did it was going to be mirrorless rather than DSLR, as even a year or so ago I could see the writing on the wall there and felt that buying another DSLR and/or lenses would not be as much of a step into the future as buying mirrorless would be. I took into consideration the kind of shooting I most like to do and the kind of camera body and lenses which would best suit that purpose. I also realized that the longer I dawdled about making a decision the more likely it was that my current lenses and bodies would continue to drop in value. That is definitely a valid concern. Time went on and just as I'd pretty much decided to go with Sony's A7R III rather than with Nikon's Z series, darned if Sony didn't release the A7R IV! So, a little more waiting as the camera was put into the hands of reviewers and eventually regular users as I weighed the pros and cons of buying an A7R III for less money now or going with the definitely-ready-for-now-and-into-the-future A7R IV. Finally one day I made up my mind for sure, packed up my Nikon gear and went to a local camera shop to do some negotiating and trading..... I came home with the Sony A7R IV and three new lenses.
All the waiting and watching and thinking about this paid off and I am very pleased with my decision and with my new camera and lenses. I miss my Nikon gear, but to be honest many of the lenses were just sitting in the Pelican case or camera bags unused most of the time, and I tended to reach for only certain lenses over and over again. Many of my lenses were older, too, including some AIS ones, and I am sure that by now they have found new homes and new users who will enjoy them as much as I did in the past.
My thought process in the end boiled down to going with Sony rather than with Nikon mirrorless because I found it disappointing that Nikon was not offering much in the way of native lenses initially, and that there was no native macro lens available, not even on the "roadmap" yet, and that also many of my lenses would only work as manual focus on the FTZ adapter. In my mid-70's I am not getting any younger and my eyes are certainly not getting any younger! I seriously prefer and need autofocus as much as possible, even with focus peaking, although that does help enormously. Aside from that I am not too keen on using adapters anyway -- I much prefer native lenses. Sony offers a good selection of native lenses that will pretty much fit into the kind of shooting I like to do. So that was my particular process.....
I do think that as time goes on more and more people will choose mirrorless over DSLRs, even for the kinds of shooting that up until now were dominated by DSLRs (wildlife, sports, etc.). Unfortunately, although the camera bodies have slimmed down and lost some weight, some of the full-frame lenses now available for mirrorless can be nearly as big and heavy as the ones for a DSLR!
Right now it is hard to predict just when the shift from DSLR to mirrorless will definitely tip predominantly to the side of mirrorless, but I do think that day is coming, and more than likely sooner rather than later. Another thing which is changing in the world of photography and which already is having an impact is the increased use of smart phones for casual snapshots and such, which has put a huge crimp in what used to be a large P&S market but also even to a certain extent affects those who once would've bought perhaps an entry-level DSLR and a lens or two as opposed to a P&S.....Some of those people are opting to use only their smartphone and not bother with carrying and using a "real" camera at all.
It is likely that in the future the only people who purchase and use "real" cameras are going to be those who are genuinely enthusiastic about photography as the wonderful art and craft that it is, or as the very functional documentary/recording of history instrument that it also is..... That is, professionals who need to shoot sports, wildlife, architecture, weddings, maternity/infant/toddler and family portraits, plus serious amateurs/enthusiasts/hobbyists who like to shoot what interests them most and who cannot imagine life without a camera in their hands.
