I jumped ship some years ago from the Nikon DSLR system to the Fujifilm X system. The reasons I presented to myself were partly practical and partly fanciful - it was the sort of thing that many enthusiasts do without any really serious thinking.
I thought that I was going to get a system that would give me the same images as before, but with smaller and lighter equipment. I convinced myself that it would be a good thing. The opportunity arose - I was working in the main shop at the time and Fujifilm prices were pitched at a deliberately low level to capture new business.
Did I change over completely? Yes - selling out all the Nikon gear over a period of a couple of years. I invested the money obtained into new Fujifilm bodies and lenses.
Did I lose some good equipment? Yes - the two D-300 camera bodies were real workhorses and the two SB 700 flashes were state-of-the-art devices that I had learned to control very well. Even the SB 600 was pretty darned sophisticated. I was getting good with them all.
Did I get good stuff as replacement? Yes. I now swear by the X-Pro1, X-T10, X-T2, and X-E2 bodies and all the lenses that I've accumulated. I use more primes than with the Nikon system but still turn to a zoom for event coverage - and it does the job admirably. I do carry a lighter camera when I am going out to do candid or reportage.
The flash system was a downgrade until the new EF-X500
came along. It is as good as the old SB 700's
but hellishly more expensive.
But did I get it all? No - I sacrificed some degree of certainty in action and dance photos with the mirror-less systems, and the lens range is restricted. I don't imagine that I'll be shooting any long telephoto stuff at the race track.
The real danger now is that I have a camera body - the X-T2 - that can be equipped with a vertical battery grip and controller. It has the attraction of holding an extra two batteries for 3 X the shooting life...and it holds them vertically so that some dance show shots are far easier to take...but it carries the risk that I will find myself with all the weight that I had before with the added expense of re-buying it.
I'm not the only one in danger - the enthusiast who buys a Sony A7R may be tempted to add the Zeiss wunderoptik instead of the Sony version and end up with a camera that is every bit as big and heavy as a DSLR. Is this always to be the evolution of newer and smaller cameras - that they grow until the rival their predecessors? Look at the heading image and judge for yourselves.
The back end of several of the cameras is similar - and welcome. The tilting and floating LCD screens started out being gimmicks and have become really useful features - it is one of the main reasons that the X-T2 is now the Little Studio camera.
Will we see more mirror-less in the future? Yes, indubitably. Will we see a Nikon version? One hopes. Will I jump ship again? No - I'm doing fine and my bank account is not as agile as it might once have been. But you can do as you see fit - just don't load your next choice down with accessory hydraulic elephant loaders and beer taps.