Seems way too soon for a successor, but firmware to allow the C100 mkii to output 4K would get a lot more people on board. Everything about the camera is nice - colours, cadence, usability - but people want some degree of future proofing.
Speaking of that :
I was just at a broadcast exhibition here in Paris, because I wanted to look at the FS5 : I have a C100 MKII and when I'm shooting doc with the ninja, it's kind of heavy setup and 4K+422HD+slowmotion+SDI RAW made me think of FS5.
BUT
a Canon REP kind of told me that a paid 4K update COULD be available for C100 MKII in the next months....