Yes, I've heard about Rubinous (the Ruby equivalent to PyPy), but it doesn't have the resources.
Basic structures like if, else, while etc. is easy. The hard part is the object model (including constant lookup) and long jumps (exceptions, next/break). Let's not forget the big core library which you need to implement if you want it to be usable at all…
Wouldn't one just point the translator/compiler to whatever Ruby's equivalent is of /usr/lib/python2.7 and let it be "turtles all the way down"?
It came a bit as a surprise to me that the author mentions jython as an example that languages on the hotspot vm don't benefit too much from its features - jruby certainly does.