Personally i think DFD is OK for photo, have not shoot any really fast action with DFD though.
The fastest sport I have shot with Panasonic DFD is soccer but that is actually as difficult as it gets for contrast autofocus. In soccer you want to take photos of where the action (ball) is and this is usually somewhere in the middle of players, some of which are running closer and some further away from you than the actual target.
Real problem is how to configure CDAF settings so that camera focuses on the correct spot between moving players and maintains focus during entire burst when the target is moving as well. I have achieved best overall results by
1) setting a fairly small AF box somewhat above the center of image (around where players heads would be in the final picture)
2) sacrificing burst speed for accuracy by selecting focus priority (there's no point to get more pictures if they are all out of focus)
3) shooting short bursts and making sure that each time I press shutter, target is exactly inside AF box and stays there during entire burst
4) selecting AFF instead of AFC.
Speed of AF per se is not a problem with any high end panny MFT body if you use new-ish panasonic/leica lenses which are optimized for DFD. Achiless heel for DFD has been C-AF which is really annoying especially when shooting video. Even when it doesn't lose focus entirely, you can see clear artifacts on out of focus areas like fences, buildings and other grid like surfaces when DFD checks whether the target is still in focus by quickly "blinking" slightly out of focus and back again. Based on reviews those new DFD algorithms on S5 are providing hughely improved C-AF performance and can be re-used on any sensor size and type as long as camera has enough processing power.
This problem is not present in stills if focus priority is selected because camera only takes pictures when they are in focus whether it takes few milliseconds more or not.