A while ago, I had the "krazy" idea of writing my own single binary Go router software on top of linux kernel. Turns out it's fairly easy to get up and running with literally having nothing but a kernel image and a single executable that gets called on boot. My kernel booted in less than 2 second on a VM.
Use LING (Erlang on Xen). Fast boot, great libraries and tools for building network applications and introspection, and still hosts its own shell (albeit an Erlang one) you could remote into if you so desired.