I've shot MLB, NFL, PAC12 football, and numerous junior college sports with a pair of D5s. That's a pretty broad set of conditions. Having switched from Canon in the summer of 2016, I'm very happy with my decision based on the last year's shooting.
The camera is a beast, but you expect that with any Dx series body. Mine have been banged around on concrete photo wells, bounced off my hip while running with a 70-200 attached and been three rain and other weather. All good.
The colors and high ISO are beautiful. I shoot RAW only, but it takes very minimal processing to pull beautiful images from it. I shoot at higher shutter speeds than my colleagues with the 1Dx2s because the high ISO is cleaner.
Is it perfect? No, there's some things I'd love to see addressed with Nikon's next flagship body.
1) Slow tagging of images when in different playback display option, namely "None". When the "basic" shot info is displayed, tagging images has virtually no lag. When shooting without any display info, there is a slight lag. I don't need to see the number of the shot or date and time; I like just the image. But it's slower this way. Tagging or locking images is a part of a very common sports workflow prior to ingesting in Photo Mechanic.While I'm on the topic, I'd love to see a way to tag "last burst". Perhaps holding the "i" button while tagging the last image of a sequence? Something like this could save a lot of time and keep the photographer focused on play instead of reviewing and tagging.
2) Eye/Face Detection in Auto AF. I use this AF mode as my "bail out" when action is coming in too close or fast to be able to select a different AF point in Single or D9. It's actually very useful and can make a keepers out of otherwise blown shots. Eye/Face detection in this mode would make it even more useful.
3) 14 fps. The 1DxII does 14 fps, it's something to catch up on. It gives you an extra frame or two in a burst to find just that precise moment for the best shot. I started out shooting manual focus in film, so I'm used to shooting a single frame. Burt technology has changed since I started shooting almost 40 years ago, and so hasn't the way sports is shot. More choices and options are better.
4) 24 megapixels or more, but under 30. The D5 is 20.8 MP, and it's files are very droppable. But using super-tele primes is standard issue for sports and wildlife, and sometimes you need to make some pretty severe crops. I've had my share of those and have them published, so at it's current 20.8, it's good. However, a few more MP would be even more flexible. However, getting too high slows download and image processing times, so something like the D850's huge files can be a bit of a bottleneck depending on application and workflow.
5) Silent shutter mode that's really silent. Shooting golf or tennis, the quieter the better. Mirrorless has an advantage in this aspect. I'll take a super quiet single frame and I'm sure some wildlife or performing arts shooters might find this useful. I've tried camera muzzles and they aren't the answer.
No major quibbles for the D5 from me. After shooting as much as I have with my two bodies, that really says a lot. Technology keeps advancing and I'm looking forward to what Nikon does with the next D series pro body, but I'm not scratching at the walls for any lack of anything essential. I have no misgivings about switching brands, even with the financial hit I took in doing so. After two years, the D5 has exceeded my expectations.