We kinda expect this one...UHS-II are very fast cards that can be up to the task for most of the photography purposes leaving the cfexpress more to video matters. However....I don´t know what to think...In one way is good, it means we can use our sd cards...On the other hand...I think cfexpress is the future coming, so we will purchase a 2020 camera that still have the "old" technology...well, we know SD cards will be around for a while but I dont see myself buying more SD cards, we need to start investing in the new cfexpress specially for video...that´s why i am a bit afraid that i will be always swapping cfexpress cards and have a useless sd slot free...because i am quite sure that the 4k and 8k video recording will be almost exclusive to cfexpress recording. And I mean almost leaving out the 4k@25fps that i believe it can be recorded to the SD cards.
Also, in stills buffer will be more limited with the UHS-II cards. If that is going to be an issue...don´t know...But it won´t be fast recording 45mp files without filling the buffer...If Canon can give us 100 raw files buffer without filling that buffer, then i guess its ok having an sd slot...