Nikon will reportedly give an update shortly on the early 2019 promise it made to D5, D850 and D500 users that it would upgrade the firmware to make their XQD card slots into CFexpress compatible slots. According to Nikon Rumors, the plan is to have this ready by the end of 2020.
While CFexpress cards may become usable, other existing bandwidth hurdles in those cameras may not allow them to fully take advantage of the blazing speeds, which may have made the fulfillment of the promise a lower priority. The review of CFexpress card readers and updated review of CFexpress cards shows that there are a lot of components that need to be optimized in order to get the good stuff.