I recently acquired a Kobol Helios 64 (Introduction - Kobol Wiki). It has a AArch64 architecture and is powered by a Rockchip RK3399.
I wonder if it鈥檚 possible to install NixOS on it. The Rockchip RK3399 is supported by the community in different boards (such as NixOS on ARM/Firefly AIO-3399C - NixOS Wiki). Is it worth a try? Does anyone have some experience on the subject? 
It is probably worth a try, generally try to follow existing work on the subject.
Stick to the wiki and (if available) existing nixos-hardware configuration options to guide you.
Based on my limited experience with arm/x86 boards with quirks, you can get it done, but it might take a bit of time. If there is prior work on the SOC, then someone hopefully got most of that done though.
I finally got the time to dig into this a but more deeply.
Unfortunately, there is not much online about running NixOS on this hardware. All I could find was this pull-request (closed, seemingly due to frustration for random/non-reproducible issues): kobol/helios64: init by samueldr 路 Pull Request #318 路 NixOS/nixos-hardware 路 GitHub
In the thread, one user (@Mic92) affirms to be running NixOS on the hardware with no issues: kobol/helios64: init by samueldr 路 Pull Request #318 路 NixOS/nixos-hardware 路 GitHub
Relevant section of the user鈥檚 config: dotfiles/machines/blob64/configuration.nix at e9f775e68744db5e56c1c6f564e6fa166f625047 路 Mic92/dotfiles 路 GitHub
None of the default NixOS sd-card images for aarch64 would boot on my Helios64. The LEDs would just turn on and nothing would happen, and I see nothing from tty. So I tried generating one following Mic92鈥檚 configuration (see above). Here is how I progressed so far: GitHub - sh4k095/nixos-helios64: NixOS sd-card image generator for Helios64 (I should add that the dedicated Armbian image boots without issues, and the device has been running it flawlessly for quite some time with ZFS, so I would exclude hardware issues).
I tried generating the image with nix build .#nixosConfigurations.helios64-installer.config.system.build.sdImage. The image builds successfully, but it won鈥檛 boot (same symptoms described above).
My experience in running NixOS on ARM is very limited, and with nothing to read from tty upon booting I am out of clues on how to get a bootable image. If you see something atrocious in my config, or have some other piece of advice, I鈥檓 all ears 