Well a subject that I would like to contribute.
I don't own the K-3 at this moment, but I did have one and went to a volleyball tournament with it:
https://www.pentaxforums.com/forums/172-pentax-k-3/246938-i-went-out-volleyball-tournament-33-images.html
Left some comments there and in general it is a better camera in technics then the K-5(IIs) is.
Is it a camera with the same options as the D4s and 1Dx are? Well not by far.
I once used the Sigma 300mm/f2.8 screwdriven lens on my K-5. And wow is that a fast lens in focussing. To my knowledge, since it's a few years ago, but no messurements the AF was about twice as fast as my DA*300mm. So the torck on the K-3 is even faster I guess it will be the winner. Much faster then SDM or Sigma's HSM. Short throw on the focusring and really superfast. So there is more to this story then just changing things in the camera.
Not all sportsimages require fast AF. I also have done sports with the K-01 and that is by no means a fast camera:
Sportsphotography has changed and moved over the past years. We want crisp sharp images that have nice background blur and isolation of the subject. This is done with mostly Full Frame camera's and long and fast lenses. So I have seen 200mm/f2.0; 300mm/f2.8; 400mm/f2.8; 500mm/f4 and 600mm/f4 lenses and the zooms like 70-200mm/f2.8 and 200-400mm/f4. This when it comes to CaNikon's own lenses. There are some Sigma's ofcourse.
The tracking function is great, but also a difficult thing to use. Getting most out of the camera will require some knowledge. This is where Pentax falls short at the moment. Also having the AF working fast enough to keep up the framerate with tracking and AF-C isn't in the same ballpark as some CaNikon's are. Improvement could be done there.
Only if Pentax wants to be in the professional sportsimages industrie, since otherwise there are some other stages where the camera can be more then adequate.
Does it need improvement?
Yes
Does it need to be as good as CaNikon's professional gear?
No
Do we need the big lenses (that go up to 10k $)?
No
Do we need Full Frame?
Well for this professional task yes, but you know that I think that APS-H is more then enough)
Should Pentax be in this professional sports image park competing?
No, but improving om camera and lenses would make the brand better for more users.