The article covers this:

> Sadly, having a microSD Express card slot on the Raspberry Pi 5 does not make a lot of sense at this point due to the cost of MicroSD Express card. An M.2 NVMe SSD is cheaper... For those reasons, [we] will not manufacture the HAT, but the design is released under a permissive MIT license, so anybody could manufacture it if needed. Maybe a microSD Express slot will make sense in a future Raspberry Pi 6, as prices come down.