edit: Actually, I spoke too soon, having trouble getting this to build. It seems the Homebrew build package has some issues at the moment.
Neovim.app isn't in Homebrew. Are you referring to its dependencies like scons, msgpack-c, or something else?
What is failing?
It builds fine for me just now on 10.10. I did have to pop in to zsh instead of fish because of `SyntaxError: Missing parentheses in call to 'print'` though. The font rendering looks a bit off for me but it's blazingly fast.
I was having trouble building the neovim package, but I did not realize that I did not have the latest command-line tools. Updating those fixed the issue.