Today as I was browsing on distrowatch, I saw a new NetBSD release.
Since it’s been some years since I last followed NetBSD, I had a
look at the wikipedia entry of NetBSD to see if something was
new.
There I saw:
https://en.wikipedia.org/wiki/NetBSD#Kernel_scripting
They appear to be using lua for scripting.
Now that may be a use case for mruby! 
Though perhaps on linux (no idea if that would work though).