XQD is an open standard supported by the Compact Flash Association just like CFast. XQD is also an upgradeable standard, unlike CFast 2.0, which is the last iteration of that standard. Sony XQD2 is same price & capacity as Arri approved Sandisk CFast2, $6.25/GB. Some (like me) will want their CFast cards to be interchangeable with Amira & Alexa.
Except in reality XQD is pretty much limited to Sony gear. There are currently FOUR cameras that use XQD. Two Nikons (D4 and D4s) and two Sonys (FS7 and PXW-Z100). Only the Sonys use XQD exclusively.
However, I wonder how this will affect the stickiness to the Canon brand when Canon needs something faster than 500Mbytes/s write and everybody needs to buy another new standard of memory cards all over again. Customers tend to sour on that. With Canon already selling 50+ MPixel cameras that time can't be too far away.
CFast 2.0 is good for up to 350MB/s real-world write. The theoretical interface limit on CFast 2.0 is 600MB/s. Those are BIG B "bytes" as opposed to little b "bits" that're used when talking about codecs. Until Canon (or anyone else) uses a codec that writes at 2800Mb/s (for current cards) or 4800Mb/s (for the interface limit) CFast 2.0 will be plenty fast.
It's very easy to get confused between MegaBYTES and MegaBITS... to convert between them:
Megabits = Megabytes x 8
Megabytes = Megabits / 8
I also find it a bit funny that people on filmmaker forums think CFast is the best thing since sliced bread, while on techie forums they are scratching their heads wondering why Canon would adapt a technology that Apple abandoned 2 years ago.
Apple never used CFast to my knowledge.
And I'm buying CFast cards knowing they will probably be completely obsolete by the time C300mk3 comes around.
I'd be willing to bet they won't. CFast 2.0 has a lot of headroom over the C300's codec.