Built in CFExpress instead of SD cards would be more useful for photographers in the future. I don't think SD will stick around in high end mirrorless cameras at least.
I expect CFExpress to become more popular in mid to high-end cameras in the next few years, but it still has relatively low penetration in consumer cameras as a whole. I know there are those who think SD cards are obsolete simply they don't personally use them, but it is still *far* more widespread (and used in different device types) than CFExpress.
Sony has taken an interesting approach with their hybrid SD/CFe Type-A readers, but they seem to be in a minority because CFExpress Type B looks set to become the standard. AFAIK, there are no hybrid readers that support SD and CFe-Type B, so at some point there might be a switch the CFe-Type B only readers on Macs. I think it will take a long time though (5+ years).
I'm not against CFExpress at at - it's a better standard, and at the high end is now cheaper than SDXC UHS-II/III. However, SDXC even if UHS-I form is good enough for a lot of people who just want to take some photos, record audio, or take FHD video. It's like USB-A - extremely widespread and good enough for the job, even if there are faster USB-C devices.