They might have indeed wanted him for Django Unleashed. Problem is, Idris signed up for Del Toro's alien/monster epic Pacific Rim. The funny thing is, I think that the two actors should switch films. Clearly, Elba is a much, MUCH stronger actor, and could really use the exposure from a Tarentino project. Meanwhile, this is probably going to be Del Toro's biggest project in terms of what it's expected to garner as a blockbuster, and could use Foxx's star-power. Oh well, both films will be excellent within their own genres.