I just downloaded it and while it looks awesome, I see the rvm problem. I haven't used zsh but I'm assuming from your comment that zsh is compatible with RVM. Seems like it shouldn't be too hard to write a fish version of the script that sets up your rvm environment, but if you've gone down that path and it proved too painful I won't bother. However, perhaps fish + rbenv works. Has anyone tried that?
Yes, I switched from rvm to rbenv because rvm didn’t work with fish. rbenv did work with fish.
I switched away from fish after that because go (a directory-jumping tool) required bash to install (http://code.google.com/p/go-tool/wiki/InstallNotes). I didn’t know how to port that bash code to fish, since I don’t know bash scripting, and I also anticipated that I would keep finding cool programs that didn’t work with fish.
The main reason for me to give it up is because I could not get it to work smoothly with rvm.
I've gotten quite used to zsh by now, and I have to say, I don't feel much for having another go at fish just to run into the same limitations again.