I think the parent is meaning something like the git-status integration of e.g. oh-my-zsh [0], or something like the 'official' git-status integration script for bash [1]
I'm fairly certain this could be defeated with a little differential cryptanalysis. Similar approaches to defeating side-channel attacks on smart card power usage have been tried and defeated :/
It'll let you use <Tab> for all the completion types, and you can tell it the fallback order for various thing (i.e. try omni, then <C-N>, etc.). It's even slightly context aware, so it can guess a good first completion method for you.
(I've used the former, but not the latter.)
[0] https://github.com/robbyrussell/oh-my-zsh [1] https://raw.github.com/git/git/master/contrib/completion/git...