Their rationale for Go is explained in the article.
> Strictly speaking, any program will do, but we need to ensure that the program in question has no dependencies on the file system. Linking it statically provides benefits. Go programs are statically linked by default, and to illustrate that the following approach works with any kind of program, we have chosen to embed a Go program into the kernel.
There were also some Java CPUs, which directly executed bytecode, in which case a "Java driver" would just be the lowest, system-level language available: https://en.m.wikipedia.org/wiki/Java_processor
