Not as polished, but I wrote something similar that leverages Google or DuckDuckGo on top of Hammerspoon. If you're in to little tweaks like this to boost your productivity on a Mac, definitely check out Hammerspoon. Hammerspoon is quite light, and runs on Lua.

Here's my version, Anycomplete: http://github.com/nathancahill/Anycomplete/

And the Show HN thread: https://news.ycombinator.com/item?id=13065670