One of the neat things about re2 is that you can walk the parsed regular expression to do crazy things with it:
It would be neat to have access to that in ruby.
Interesting; I've not looked into this part of re2 previously. Do you have a rough idea of how you'd like the API to look or do you just want it to mirror the C++ interface?
I don't have a strong feel for what would make the most sense there.
Maybe starting close to the C++ interface would be a good start.