
Plans, definitely yes. Especially as MacRuby is getting closer to a fully supported ahead of time compiler (AOT). So after my current C++ iPhone project (= maybe 2009 ;)), I will definitely look into it so I can churn out mobile Ruby games. Other Mac users will also rejoice that their precious Ruby code is finally delivered to players in something else than plaintext form.
As far as I can tell, there are currently two roads to MacRuby; either supporting the FFI interface or being an Objective C library. Since FFI sounds like something that will never work on the iPhone, the Objective C interface would make more sense (and be pretty easy to write), but I have no idea how one would statically link it against MacRuby. If you want to get your hands dirty, you can write an Objective C wrapper and see how far you get :)