When you think about it ccache is a simple feature, however we shouldn't underestimate it's power. This tool is very handy for improving waiting time and resource usage. Even if nowadays a lot of computational power and resources a simple tool like this can make a huge difference in big or even small projects. In my opinion this tool is a MUST in every compiler.
After looking at the tool that is available for C/C++ i can say for sure that we can implement this in Mono. Thanks to the deterministic inputs from Roslyn this won't be a pain in the back and we can simply port the libraries from C++ or make our own.