According to Hector Martin in the last progress report, the Wifi driver is up next, then some not terribly demanding work on various drivers (like adapting the NetBSD driver for the real time clock, and getting the M1 iMac SKU with four USB ports to see all four) after which he will tackle the kernel driver for the GPU.

https://asahilinux.org/2021/12/progress-report-oct-nov-2021/

As an interesting aside, in the progress report he mentions that after he installed Arch Linux, even without support for the hardware GPU:

>glxgears has no right to run at >60FPS with software rendering, but it does