Calling Compact Flash cards "a thing of the past" is pretty harsh and not accurate. The D810 and a number of its contemporaries from other makers use these cards, and they provide good performance in those cameras. The D810 still has factory support at Nikon (at least for now), and I'm sure that many of those other camera models do, as well.

Brand new CF cards with good capacities are readily available at my local suppliers, even if my local camera shops don't have them. What is problematic is finding lower capacity cards (16GB and smaller) for older cameras which may not be able to use the higher capacity cards.

What I have found interesting is that the price for XQD cards has increased way beyond what would be expected for a commodity memory product. These have apparently become a specialty niche product because Sony has chosen (or is not able) to enable its cameras for CFExpress cards. Single-channel XQD cards are significantly more expensive than equivalent-capacity dual-channel CFE cards of equal capacity.

I did a little search and found that CF cards are used in all sorts of current-generation instrumentation, including medical equipment. It also seems to still be one of the preferred memory formats for high-end audio recording equipment and any number of other applications. So I think it is a little bit narrow to call the format yesterdays storage just because camera makers are moving to smaller formats.

My guess is that the Type B format represents a transitory phase as chosen camera memory. Designers, manufacturers, and users have already been spoiled by the much smaller and less expensive form factor of SD and Micro SD cards. Think what they could do with the space freed up...they could add a second processor. Quite frankly, the fact that cameras even still have removable memory cards is something of a Luddite holdover in a world where excellent alternatives for wireless transfer (even via a dock of some sort) have been available for years. Of course, including something like this would risk eliminating at least or 6 lines of discussion around care, feeding, and fixing of memory cards here and elsewhere.

The point of using CF Express Type B is purely speed and capacity. They are used for video formats that require write speeds greater than 600 Mbps. Current real world SDXC speeds top out at or below that.

When you need a bit rate of 1.9 Gbps for 5.7K/30P cinema format Apple ProRes 4:2:2 HQ video, CF Express Type B version 2.0 cards are a good choice.

I WISH the SD standard supported speeds that fast! Many cameras now support connectivity to external SSD drives via USB-C (i.e.; Samsung T7 drives). However, these drives are not as fast as CF Type B cards.