CFExpress + UHS-II slots is smart at this stage. UHS-II cards are fast enough for most things that anyone shoots. Though if you want to shoot 8K video you may want to buy a BIG CFExpress card.
For over two years now I’ve been saying to friends, if another 5D gets released Canon will call it the 5DX and not a 5D V.
My reasoning is that’s what happen with the 1D series.