Having a serial connection when tinkering with network config was absolutely crucial for me.
Sources: https://discourse.nixos.org/t/do-you-use-nixos-on-your-route...
It's a bit long, but the title sections should let you skip to the interesting bits.
Here's the latest code as well: https://github.com/skogsbrus/os
Having a serial connection when tinkering with network config was absolutely crucial for me.