This reminds me of HipHop for PHP. HipHop lowers PHP to C++, with a direct mapping for control flow (control structures, exceptions) and a runtime library for everything else. Apparently it works very well.
Edit: looks like JRuby can/does do JIT compilation, but it is also capable of doing AOT compilation[2]. If JRuby can do AOT, then what is the point of FastRuby?
[0]: http://pypy.org/
[1]: http://morepypy.blogspot.com.au/2012/07/hello-everyone.html
My goal with fastruby is more to have a still dynamically-typed Ruby-like language without requiring anything more than virtual invocation and a modest runtime library (that can be statically optimized to only what's needed by e.g. Android toolchain).