Well, Rubinius is quite faster than MRI Ruby (still not as fast as C). Although, I don't like your long prognosis, I love the attitude!
However, I have never seen the problem in writing C extensions for Ruby when I am pressed for speed. Only complaint that I can think of is that my first extension was "problematic" in terms of not being able to find any resources, which made me resort to reading the source, which in turn made me a better Rubyist!
I think what's ultimately going to be needed is better profiling tools and an easy-to-use extension DSL that's designed to hook into Ruby. That way we could experiment with different structures than hash maps and still keep good Ruby style.
However, I have never seen the problem in writing C extensions for Ruby when I am pressed for speed. Only complaint that I can think of is that my first extension was "problematic" in terms of not being able to find any resources, which made me resort to reading the source, which in turn made me a better Rubyist!