But this is a £3.5k camera. It's hardly lower end..
Yes I know, but it is comparative, compared to the Canon 1D X Mark II it is the top of their mid range and not their top end.
Again who knows how Canon decided on not to include CFast cards? It might be down to who the Camera is aimed at.
Canon 5D Mark II users who perhaps didn't see the need four years ago to upgrade to the Mark III? Serious enthusiast photographers? Semi-professionals?
The 1D X has only recently been released itself, it has one CFast slot. Isn't this the first time that type of card has been put into a Canon DSLR? As I keep saying, they differentiate their models and whilst it would be nice to have the same thing on the 5DMKIV, they're a combination of marketing decisions and user feedback.
CFast cards are without doubt much faster, but they're also more expensive e.g.
Sandisk 64Gb CFast card can be had for £188 (that's the 515MB/s card)
Sandisk 64gb CF Extreme Pro card can be had for £74 (that's the 160MB/s card)
If Canon are aiming for top end enthusiasts then perhaps their though process was 'well they'll probably have quite a few CF cards, lets not make them replace all their cards well' - until next time. That's only my view though. Until someone, perhaps DPreview, interviews the CEO or Head of Design at Canon and asks them, we'll never know for sure.
That said, even if they do interview them and ask them directly, Canon execs aren't as chatty as say Mr Kazuto Yamaki the CEO of Sigma