I'd agree with the hackaday commenters that this seems like they considered putting eMMC (or any kind of flash) storage on the high-end board. Would have been nice considering the reliability of most microSD cards.
They will need to offer a 64-bit kernel then. It's unfortunate that even the newest Raspbian for the Pi 4 is still 32-bit, both kernel and userland.
Given all the efforts to cram Visual Studio Code onto the Pi (because kids learning the basics of programming need a "modern" development environment), an 8 GiB Pi would actually make that practical.