It's still not really ready for prime-time, but I've got a M1 mac mini running debian as an arm64 build bot (and a few other small things) now, and I can say that the bits that work, work really well. Storage is fast, CPU performance is solid, PCIe for ethernet works just fine. Now if I could just get one with 64G of RAM and 2TB of SSD... ;) edit: the setup process is still far from polished but that's not unexpected…
Careful what you wish for. With the way Apple marks up memory and storage upgrades, you might be looking at a $5,000 machine there...