I think there has been a LOT of discussion about setting aside a DSLR kit in favor or a mirrorless system. Specifically, I'd like opinions from those who shoot mirrorless if I should trade my DSLR Kit for a mirrorless kit.
I currently have:
D300 with grip/batts/memory cards
Tokina 12 - 24 f4
Nikon 35 - 70 f 2.8
Nikon 50mm f 1.8
Nikon 85mm f 1.8
Nikon 70 - 300 VR
Nikon 18 - 55 (not used)
2 ea Nikon SB600 flashes
I am thinking about a kit built around the Fuji xt1 and 18 - 55 lens. I would need a long lens for still/video of my daughter playing soccer. I'd also like a fast prime for walking around/travel etc.
I do some travel/documentary, documentary, my kids sports, and quite a bit of protrait work (family, kids, seniors) plus some landscape.
Three options I am considering.
1. Trading the entire Nikon kit for the Fuji
2. Selling off the camera body/grip/batts and cards + the Tokina WA lens and buying a Nikon D610 body
3. Keeping the current gear until after Photokina and possibly new Nikon bodies coming out.
Thoughts?
I've spent a LOT of time with both DSLRs and mirrorless cameras in the past decade.
DSLRs, particularly at the AA and Pro end of the scale (like your D300) are highly optimized for responsiveness (by minimized shutter lag, by quick exposure-to-exposure cycling, by highly developed autofocus, etc etc) and are still the best tools for use with action subjects.
There's a fundamental issue here. An optical viewfinder system operates at the speed of light, and a single-lens reflex system displays images at the speed of light gated by the flipping mirror—in shooting a sequence of images, you get to see an image between exposures in the brief flip of the mirror BEFORE the exposure is made, which is enough to predict subject movement and judge the peak of the action. An EVF can never be that fast, and its brief flicker of the subject has to necessarily FOLLOW the exposure, so it can never be used predictively. This is most visible in sequence shooting, but its impact can be felt in single frame exposures too.
With that understanding, few folks really push their equipment to the level that this is a significant issue with the current high-end generation of 'mirrorless' cameras. The most responsive mirrorless camera to date is the Olympus E-M1, which gives up very little to the pro-grade Olympus E-5 in responsiveness. I haven't worked with the Fujis enough to have an opinion of them there, but I have had Olympus E-1, E-5, and E-M1 at the high end of their spectrum and there's very little I cannot accomplish more easily with the E-M1 that I could do with E-5 except for this and one other thing ...
With very high magnification lenses, again the speed of an optical viewfinder vs the speed of an EVF can be an issue. The behavior here is that with an optical viewfinder, the movement of the camera as seen through the viewfinder is not complicated or magnified by the scan-line delay timing inherent in an electronic viewfinder. It just jumps around a little. With an electronic viewfinder, the movement of the camera can be exaggerated to the point of unusable by the display flickering and 'tearing' due to the display refresh cycles.
I see this with the Sony A7 when I fit lenses 135mm and longer. I have to take pains to hold the camera very still, or mount it on a tripod, so the viewfinder image is presented steadily enough for critical focusing. It's much more difficult to stabilize for focusing than fitting a manual lens of equivalent focal length to the Olympus E-1 or E-5 with respect to focusing. The Olympus E-M1 ameliorates this situation a good bit by having exceptionally good in-body-image-stabilization, which allows nearly any lens to be stabilized for focusing easily (although it seems it's not quite up to the challenges of my friend's 750mm astro-scope).
For the other things that you mention—portraits, travel, travel/documentary, documentary, still life, architecture, etc—the best of current mirrorless cameras produce equivalent functionality and imaging qualities compared to the DSLRs. What sports you're shooting, and HOW you shoot them, are often the critical line that you have to evaluate which camera is going to be most feasible for your use.
For my use, I have a three-body system: I kept my ancient Olympus E-1 and a small selection of FourThirds lenses for those specific moments when its shooting responsiveness, particularly with long lenses like the 50-200 plus teleconverter, is required.
For most other shooting with full automation, the E-M1 body with the same FT lenses as above, as well as a nice range of compact and light Micro-FourThirds prime lenses, does a brilliant job.
For my prized collection of favorite Nikon F mount and Leica R mount lenses, I bought the Sony A7 to shoot with. It's a more compact body than any current DSLR, has a better viewfinder than any of the ones at its price level, and is the full-frame original format that these lenses were designed for. These lenses work very well on its sensor. (The A7 and A7r are not great with many of the M-mount lenses, although a few of mine do work satisfactorily giving me a compact kit when so desired.)
Exactly what mix of equipment does the best job for your needs and desires ... I cannot say. But one thing is for certain: no one camera does everything best.
G