It being included will have no performance overhead since it's only loaded if it's used.

I'm personally for this idea, I've used DJ, Resque and Sidekiq, all in the same project (increasing load), and in that order; It would have been much nicer to have to only change the Gemfile when I made the switch.

Your comment, whilst a perfectly valid concern, reminds me of an article DHH posted: http://david.heinemeierhansson.com/2012/rails-is-omakase.htm...