My $.02 on why I won't be buying either the S800 or Zenmuse...
I'm not a big fan of closed source systems which is essentially what DJI is turning out to be, they keep the software locked up on their servers and many of the bits on the S800 are unique to it beyond just the frame itself, i.e. the motors and props. From my perspective I'd rather be able to use generic parts bought from any number of vendors rather than be reliant on parts availability from just one source and I much prefer being able to carry copies of the software on my laptop so if needed I can reload anywhere, anytime, without having to connect to a server thousands of miles away to do it. The extension of the closed source philosophy is the apparent requirement for a connection to a WKM controller to be able use the Zenmuse, a restriction that is a deal breaker for me, I like being able to mix and match components across all of the hardware I currently have.
While I really like they way the WKM flys in good conditions there are too many limitations for me to consider it to be the primary flight control system I'm going to go with. MK may not be quite as good at a couple of things as the WKM, but I think overall Mk is the better choice for an open source solution as well as lower total cost of ownership when you factor in what you get for free in the MK software vs having to pay big $$$$ for the same capability with DJI. In light of the recent improvements in the MK firmware I find myself flying the Mk platforms more than the DJI lately, not that I plan to stop using either the WKM or Naza or sell them off anytime soon, just that I feel DJI is heading in a direction I don't want to go and I believe I get more value for my $ with MK.
Ken