Good question, guess the timing to adopt the new standard depends on personal requirements and limitations.
My D500 and Z6 are not going anywhere anytime soon, might add a second Zee camera to the collection to replace the Sony a7S but I see no point in selling these two gems. Both use XQD and work best with these cards, CFexpress can be used but are slower and have a smaller buffer size as a result.
Then there’s the lack of suitable future proof readers, don’t mind spending money but hate wasting it unnecessary. I mainly use the iPad Pro 12.9 2020 for my photo editing so out of the four dual format readers the three thunderbolt 3 readers are out by default, also the XQD fix won’t work on iOS and the two readers with confirmed solid performance by trusted forum members are heavy duty desktop models not suitable for travel.
The Sony is USB-C and suitable for travel but two members here reported issues plus it is not fast enough to use the cards at their max speed potential on the Macbook which kind of defeats the point of using these cards when the camera’s can’t utilize the extra speed neither.
This leaves the two single format readers from Transcend and Lexar:
https://www.bhphotovideo.com/c/products/Card-Readers/ci/1096/N/4093113321?filters=fct_a_memory-card-type_5618%3Acfexpress%2Cfct_usb-version_7132%3Ausb-3.2-20-gb-sThese are both USB-C for the iPad Pro and fast enough to read the 1700MB/a cards on the MacBook Pro at full speed because they are USB 3.2 2x2 which supports 20Gbps transfer speeds. The fact that they cost less than the cards themselves is also a nice bonus, they are future proof as USB4 is backwards compatible with older protocols but the downside is traveling with multiple readers when both cameras come along for the ride.
But it’s still early stages and I am in no rush so will probably buy a CFexpress card when the first travel size dual format USB4 readers come to market like I just did for my NVMe M.2 SSD cards.
That all being said, buying CFexpress cards when owning the latest cameras which natively support them is a no brainer, just be aware which reader you buy