alt Hacker NewsNVMe hats work in OpenBSD, it's NVMe boot that doesn't work at present. It still needs support added to the U-Boot firmware, which OpenBSD uses here. Raspbian and other Linux distros are typically booted differently on this hardware (Linux kernel image is loaded directly by the GPU, not joking.)
Also, Wi-Fi is supported on some Raspberry Pi 5 models, with the bwfm(4) Broadcom driver. It's just the later D0 hardware stepping that doesn't, C1 works fine.
https://marc.info/?l=openbsd-cvs&m=175526487704135&w=2
I believe Ethernet may also be working via the cad(4)/Cadence driver, but I don't have the hardware to test it.
Linux kernel image or another stage of bootloader loaded by the GPU is pretty normal in mobile SOCs like the one that is used here. At least they did not enable secure boot so that it's still possible to execute something else.