It might have been a concept for a wilderness miniboss. I haven't heard very much about it, though, and as far as I am aware it hasn't been implemented into any version of the game, including publicly released test builds. While I'd be down for more threatening Wilderness enemies that were like bosses, that seems to be what Fish has been doing with Elite enemies (he once stated that he wants to give each Elite variant a Unique AI pattern that differentiates them more from their normal version). Guess we'll have to wait and see what Fish has to say on the matter!