The original interpreter is already replaced with YARV in 1.9. But yes, MacRuby replaces YARV with an LLVM-based virtual machine. (Only passes about 85% of RubySpec right now, though.)

Incidentally, Rubinius is also based on LLVM these days.

Such a fundamental changes like unladen swallow in python or migrating to LLVM-based VM in ruby must be backed by very powerful and resourceful entity. Good news!