Given the lack of activity on the official Exuberant Ctags source, it has been forked and renamed to Universal Ctags and can be found at https://github.com/universal-ctags/ctags.
brew install --HEAD universal-ctags/universal-ctags/universal-ctags
When Universal Ctags has a tagged release, this formula should be moved
to the official Homebrew repository. The formula should then be deleted
from this repo and a tap_migrations.json file be added to ensure an
automatic transition for existing users of the formula.