Canon almost had no choice.
If they put CF in the 5D4, they would be using an old technology that is maxed out on speed which would be expected to compete with other cameras for the next 4 years. That's not going to work.
They have the option of either:
XQD
CFast
SD UHS-II
Any combination of the above. They don't want to use Sony's card, so that's out. That leaves very little choice.
Dual CFast, which would annoy many as they'd be forced to use these expensive cards. Not even the 1DX2 uses two of them. So that's out.
Dual SD UHS-II. This I would have preferred. Smaller cards. Just as reliable as CF if not more. Lower costs. Plenty fast for whatever this camera is going to put out. Backward compatible with older SD formats.
CFast + SD UHS-II which is what this rumor is about and the most likely combo. Canon feels it will have to provide at least one super high speed card. But I think it is more industry reaction. There's too many out there that attribute the physical size and characteristics of CF and CFast to reliability and robustness. Sure, I'll agree the C cards are tougher than SD which is smaller and flimsier. But c'mon already - who subjects their cards to physical abuse? Who has snapped an SD card? If you break an SD card due to physical abuse, you're probably not using any electronic device successfully. Bizarre concerns here.
The key here is that C cards are associated with "professional" quality/speed in the minds of pros and semi-pros and even some enthusiasts, so Canon is reacting to this in their semi-pro camera. They aren't basing this on technological fact but rather market perception in my opinion. Nikon doesn't mind using dual SD in the D750 which while might not be labeled pro or semi-pro, is in quality and features, at least a semi-pro to pro camera.
The C cards take up so much space in a camera body - I'd like to see one day a DSLR go to an SSD with an SD card as a backup/removable. 512gb or larger SSD. Either internal, or again, because the C slot take up so much space, a servicesabe one could be incorporated. It wouldn't be a card to be regularly removed, but removable for service if need be. (not soldered onto the mainboard).
Some hate this idea as they would have to then tether the camera via USB or whatever interface to dump the photos or video. I don't see why this is a problem. With CFast and UHS-II you need a new card reader(s) to take advantage of any of the speed. And these card readers all interface via USB-3 anyway. So you're stuck with extra cables anyhow as well as extra cost. Don't count on any laptop or PC having a CFast port on it anytime ever.
A camera with a USB-C port would be great. Smaller and more universal than USB-3. Or, a Thunderbolt port, which is compatible and the same as the modern DisplayPort. This is even faster, and can also carry video at data rates much faster than the lame HDMI standard. HDMI is finicky and unreliable - and can barely put out the top 4K qualities. DP easily does it. The physical port is smaller too and more robust.
I'd rather have a simple cable to connect my camera to PC, than have to buy another card reader. The transfer speed will be faster than having to involve a middleman card reader interface.
People will say built in SSD would be expensive. Compared to what? CFast is pricy. As is XQD. These are essentially mid-level SSD's in a easily removable form factor. Costs more to make them quick swappable. Card costs, card reader cost, then interface costs for manufacture. This cannot be cheaper than SSD.
One downside, and I see this as a very minimal downside are some event shooters that say they need to upload photos quick while continuing the shoot. Handing over cards to an associate who is publishing on site. This sounds like less of a card problem, and more of a need for a wireless transfer solution. Canon has an wireless transfer module that does just that.
;D
